opt_subselect.cc 162 KB
Newer Older
1 2 3 4
/**
  @file

  @brief
5
    Semi-join subquery optimizations code
6 7 8 9 10 11 12 13 14 15 16 17 18

*/

#ifdef USE_PRAGMA_IMPLEMENTATION
#pragma implementation				// gcc: Class implementation
#endif

#include "mysql_priv.h"
#include "sql_select.h"
#include "opt_subselect.h"

#include <my_bit.h>

19 20 21 22 23 24 25 26 27 28 29 30 31 32
/*
  This file contains optimizations for semi-join subqueries.
  
  Contents
  --------
  1. What is a semi-join subquery
  2. General idea about semi-join execution
  2.1 Correlated vs uncorrelated semi-joins
  2.2 Mergeable vs non-mergeable semi-joins
  3. Code-level view of semi-join processing
  3.1 Conversion
  3.1.1 Merged semi-join TABLE_LIST object
  3.1.2 Non-merged semi-join data structure
  3.2 Semi-joins and query optimization
psergey's avatar
psergey committed
33 34
  3.2.1 Non-merged semi-joins and join optimization
  3.2.2 Merged semi-joins and join optimization
35 36 37 38 39 40 41 42 43 44 45 46 47 48 49
  3.3 Semi-joins and query execution

  1. What is a semi-join subquery
  -------------------------------
  We use this definition of semi-join:

    outer_tbl SEMI JOIN inner_tbl ON cond = {set of outer_tbl.row such that
                                             exist inner_tbl.row, for which 
                                             cond(outer_tbl.row,inner_tbl.row)
                                             is satisfied}
  
  That is, semi-join operation is similar to inner join operation, with
  exception that we don't care how many matches a row from outer_tbl has in
  inner_tbl.

50 51
  In SQL terms: a semi-join subquery is an IN subquery that is an AND-part of
  the WHERE/ON clause.
52 53 54

  2. General idea about semi-join execution
  -----------------------------------------
55 56
  We can execute semi-join in a way similar to inner join, with exception that
  we need to somehow ensure that we do not generate record combinations that
57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103
  differ only in rows of inner tables.
  There is a number of different ways to achieve this property, implemented by
  a number of semi-join execution strategies.
  Some strategies can handle any semi-joins, other can be applied only to
  semi-joins that have certain properties that are described below:

  2.1 Correlated vs uncorrelated semi-joins
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Uncorrelated semi-joins are special in the respect that they allow to
   - execute the subquery (possible as it's uncorrelated)
   - somehow make sure that generated set does not have duplicates
   - perform an inner join with outer tables.
  
  or, rephrasing in SQL form:

  SELECT ... FROM ot WHERE ot.col IN (SELECT it.col FROM it WHERE uncorr_cond)
    ->
  SELECT ... FROM ot JOIN (SELECT DISTINCT it.col FROM it WHERE uncorr_cond)

  2.2 Mergeable vs non-mergeable semi-joins
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Semi-join operation has some degree of commutability with inner join
  operation: we can join subquery's tables with ouside table(s) and eliminate
  duplicate record combination after that:

    ot1 JOIN ot2 SEMI_JOIN{it1,it2} (it1 JOIN it2) ON sjcond(ot2,it*) ->
              |
              +-------------------------------+
                                              v
    ot1 SEMI_JOIN{it1,it2} (it1 JOIN it2 JOIN ot2) ON sjcond(ot2,it*)
 
  In order for this to work, subquery's top-level operation must be join, and
  grouping or ordering with limit (grouping or ordering with limit are not
  commutative with duplicate removal). In other words, the conversion is
  possible when the subquery doesn't have GROUP BY clause, any aggregate
  functions*, or ORDER BY ... LIMIT clause.

  Definitions:
  - Subquery whose top-level operation is a join is called *mergeable semi-join*
  - All other kinds of semi-join subqueries are considered non-mergeable.

  *- this requirement is actually too strong, but its exceptions are too
  complicated to be considered here.

  3. Code-level view of semi-join processing
  ------------------------------------------
  
psergey's avatar
psergey committed
104 105
  3.1 Conversion and pre-optimization data structures
  ---------------------------------------------------
106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121
  * When doing JOIN::prepare for the subquery, we detect that it can be
    converted into a semi-join and register it in parent_join->sj_subselects

  * At the start of parent_join->optimize(), the predicate is converted into 
    a semi-join node. A semi-join node is a TABLE_LIST object that is linked
    somewhere in parent_join->join_list (either it is just present there, or
    it is a descendant of some of its members).
  
  There are two kinds of semi-joins:
  - Merged semi-joins
  - Non-merged semi-joins
   
  3.1.1 Merged semi-join TABLE_LIST object
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Merged semi-join object is a TABLE_LIST that contains a sub-join of 
  subquery tables and the semi-join ON expression (in this respect it is 
psergey's avatar
psergey committed
122
  very similar to nested outer join representation)
123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139
  Merged semi-join represents this SQL:

    ... SEMI JOIN (inner_tbl1 JOIN ... JOIN inner_tbl_n) ON sj_on_expr
  
  Semi-join objects of this kind have TABLE_LIST::sj_subq_pred set.
 
  3.1.2 Non-merged semi-join data structure
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Non-merged semi-join object is a leaf TABLE_LIST object that has a subquery
  that produces rows. It is similar to a base table and represents this SQL:
    
    ... SEMI_JOIN (SELECT non_mergeable_select) ON sj_on_expr
  
  Subquery items that were converted into semi-joins are removed from the WHERE
  clause. (They do remain in PS-saved WHERE clause, and they replace themselves
  with Item_int(1) on subsequent re-executions).

psergey's avatar
psergey committed
140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165
  3.2 Semi-joins and join optimization
  ------------------------------------
  
  3.2.1 Non-merged semi-joins and join optimization
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  For join optimization purposes, non-merged semi-join nests are similar to
  base tables - they've got one JOIN_TAB, which can be accessed with one of
  two methods:
   - full table scan (representing SJ-Materialization-Scan strategy)
   - eq_ref-like table lookup (representing SJ-Materialization-Lookup)

  Unlike regular base tables, non-merged semi-joins have:
   - non-zero JOIN_TAB::startup_cost, and
   - join_tab->table->is_filled_at_execution()==TRUE, which means one
     cannot do const table detection or range analysis or other table data-
     dependent inferences
  // instead, get_delayed_table_estimates() runs optimization on the nest so that 
  // we get an idea about temptable size
  
  3.2.2 Merged semi-joins and join optimization
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   - optimize_semijoin_nests() does pre-optimization 
   - during join optimization, the join has one JOIN_TAB (or is it POSITION?) 
     array, and suffix-based detection is used, see advance_sj_state()
   - after join optimization is done, get_best_combination() switches 
     the data-structure to prefix-based, multiple JOIN_TAB ranges format.
166 167 168 169

  3.3 Semi-joins and query execution
  ----------------------------------
  * Join executor has hooks for all semi-join strategies.
psergey's avatar
psergey committed
170 171
    TODO elaborate.

172 173 174
*/


175 176 177 178 179
static
bool subquery_types_allow_materialization(Item_in_subselect *in_subs);
static bool replace_where_subcondition(JOIN *join, Item **expr, 
                                       Item *old_cond, Item *new_cond,
                                       bool do_fix_fields);
Igor Babaev's avatar
Igor Babaev committed
180 181
static int subq_sj_candidate_cmp(Item_in_subselect* el1, Item_in_subselect* el2,
                                 void *arg);
182
static bool convert_subq_to_sj(JOIN *parent_join, Item_in_subselect *subq_pred);
183 184
static bool convert_subq_to_jtbm(JOIN *parent_join, 
                                 Item_in_subselect *subq_pred, bool *remove);
185
static TABLE_LIST *alloc_join_nest(THD *thd);
186
static uint get_tmp_table_rec_length(Item **p_list, uint elements);
unknown's avatar
unknown committed
187
static double get_tmp_table_lookup_cost(THD *thd, double row_count,
unknown's avatar
unknown committed
188
                                        uint row_size);
unknown's avatar
unknown committed
189
static double get_tmp_table_write_cost(THD *thd, double row_count,
unknown's avatar
unknown committed
190
                                       uint row_size);
191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207
bool find_eq_ref_candidate(TABLE *table, table_map sj_inner_tables);
static SJ_MATERIALIZATION_INFO *
at_sjmat_pos(const JOIN *join, table_map remaining_tables, const JOIN_TAB *tab,
             uint idx, bool *loose_scan);
void best_access_path(JOIN *join, JOIN_TAB *s, 
                             table_map remaining_tables, uint idx, 
                             bool disable_jbuf, double record_count,
                             POSITION *pos, POSITION *loose_scan_pos);

static Item *create_subq_in_equalities(THD *thd, SJ_MATERIALIZATION_INFO *sjm, 
                                Item_in_subselect *subq_pred);
static void remove_sj_conds(Item **tree);
static bool is_cond_sj_in_equality(Item *item);
static bool sj_table_is_included(JOIN *join, JOIN_TAB *join_tab);
static Item *remove_additional_cond(Item* conds);
static void remove_subq_pushed_predicates(JOIN *join, Item **where);

208 209 210
enum_nested_loop_state 
end_sj_materialize(JOIN *join, JOIN_TAB *join_tab, bool end_of_records);

211

212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279
/*
  Check if Materialization strategy is allowed for given subquery predicate.

  @param thd           Thread handle
  @param in_subs       The subquery predicate
  @param child_select  The select inside predicate (the function will
                       check it is the only one)

  @return TRUE  - Materialization is applicable 
          FALSE - Otherwise
*/

bool is_materialization_applicable(THD *thd, Item_in_subselect *in_subs,
                                   st_select_lex *child_select)
{
  st_select_lex_unit* parent_unit= child_select->master_unit();
  /*
    Check if the subquery predicate can be executed via materialization.
    The required conditions are:
    0. The materialization optimizer switch was set.
    1. Subquery is a single SELECT (not a UNION).
       TODO: this is a limitation that can be fixed
    2. Subquery is not a table-less query. In this case there is no
       point in materializing.
    2A The upper query is not a table-less SELECT ... FROM DUAL. We
       can't do materialization for SELECT .. FROM DUAL because it
       does not call setup_subquery_materialization(). We could make 
       SELECT ... FROM DUAL call that function but that doesn't seem
       to be the case that is worth handling.
    3. Either the subquery predicate is a top-level predicate, or at
       least one partial match strategy is enabled. If no partial match
       strategy is enabled, then materialization cannot be used for
       non-top-level queries because it cannot handle NULLs correctly.
    4. Subquery is non-correlated
       TODO:
       This condition is too restrictive (limitation). It can be extended to:
       (Subquery is non-correlated ||
        Subquery is correlated to any query outer to IN predicate ||
        (Subquery is correlated to the immediate outer query &&
         Subquery !contains {GROUP BY, ORDER BY [LIMIT],
         aggregate functions}) && subquery predicate is not under "NOT IN"))

    (*) The subquery must be part of a SELECT statement. The current
         condition also excludes multi-table update statements.
  A note about prepared statements: we want the if-branch to be taken on
  PREPARE and each EXECUTE. The rewrites are only done once, but we need 
  select_lex->sj_subselects list to be populated for every EXECUTE. 

  */
  if (optimizer_flag(thd, OPTIMIZER_SWITCH_MATERIALIZATION) &&      // 0
        !child_select->is_part_of_union() &&                          // 1
        parent_unit->first_select()->leaf_tables.elements &&          // 2
        thd->lex->sql_command == SQLCOM_SELECT &&                     // *
        child_select->outer_select()->leaf_tables.elements &&           // 2A
        subquery_types_allow_materialization(in_subs) &&
        (in_subs->is_top_level_item() ||                               //3
         optimizer_flag(thd,
                        OPTIMIZER_SWITCH_PARTIAL_MATCH_ROWID_MERGE) || //3
         optimizer_flag(thd,
                        OPTIMIZER_SWITCH_PARTIAL_MATCH_TABLE_SCAN)) && //3
        !in_subs->is_correlated)                                       //4
   {
     return TRUE;
   }
  return FALSE;
}


280 281 282
/*
  Check if we need JOIN::prepare()-phase subquery rewrites and if yes, do them

Sergey Petrunya's avatar
Sergey Petrunya committed
283 284 285 286
  SYNOPSIS
     check_and_do_in_subquery_rewrites()
       join  Subquery's join

287 288
  DESCRIPTION
    Check if we need to do
Sergey Petrunya's avatar
Sergey Petrunya committed
289
     - subquery -> mergeable semi-join rewrite
290 291
     - if the subquery can be handled with materialization
     - 'substitution' rewrite for table-less subqueries like "(select 1)"
Sergey Petrunya's avatar
Sergey Petrunya committed
292 293 294
     - IN->EXISTS rewrite
    and, depending on the rewrite, either do it, or record it to be done at a
    later phase.
295 296

  RETURN
Sergey Petrunya's avatar
Sergey Petrunya committed
297 298
    0      - OK
    Other  - Some sort of query error
299 300 301 302 303 304
*/

int check_and_do_in_subquery_rewrites(JOIN *join)
{
  THD *thd=join->thd;
  st_select_lex *select_lex= join->select_lex;
305
  st_select_lex_unit* parent_unit= select_lex->master_unit();
306
  DBUG_ENTER("check_and_do_in_subquery_rewrites");
307 308 309 310 311 312 313 314

  /*
    IN/ALL/ANY rewrites are not applicable for so called fake select
    (this select exists only to filter results of union if it is needed).
  */
  if (select_lex == select_lex->master_unit()->fake_select_lex)
    DBUG_RETURN(0);

315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330
  /*
    If 
      1) this join is inside a subquery (of any type except FROM-clause 
         subquery) and
      2) we aren't just normalizing a VIEW

    Then perform early unconditional subquery transformations:
     - Convert subquery predicate into semi-join, or
     - Mark the subquery for execution using materialization, or
     - Perform IN->EXISTS transformation, or
     - Perform more/less ALL/ANY -> MIN/MAX rewrite
     - Substitute trivial scalar-context subquery with its value

    TODO: for PS, make the whole block execute only on the first execution
  */
  Item_subselect *subselect;
Michael Widenius's avatar
Michael Widenius committed
331
  if (!(thd->lex->context_analysis_only & CONTEXT_ANALYSIS_ONLY_VIEW) && // (1)
unknown's avatar
unknown committed
332
      (subselect= parent_unit->item))                                    // (2)
333 334
  {
    Item_in_subselect *in_subs= NULL;
335 336 337 338 339 340 341 342 343 344 345 346 347
    Item_allany_subselect *allany_subs= NULL;
    switch (subselect->substype()) {
    case Item_subselect::IN_SUBS:
      in_subs= (Item_in_subselect *)subselect;
      break;
    case Item_subselect::ALL_SUBS:
    case Item_subselect::ANY_SUBS:
      allany_subs= (Item_allany_subselect *)subselect;
      break;
    default:
      break;
    }

348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377

    /* Resolve expressions and perform semantic analysis for IN query */
    if (in_subs != NULL)
      /*
        TODO: Add the condition below to this if statement when we have proper
        support for is_correlated handling for materialized semijoins.
        If we were to add this condition now, the fix_fields() call in
        convert_subq_to_sj() would force the flag is_correlated to be set
        erroneously for prepared queries.

        thd->stmt_arena->state != Query_arena::PREPARED)
      */
    {
      /*
        Check if the left and right expressions have the same # of
        columns, i.e. we don't have a case like 
          (oe1, oe2) IN (SELECT ie1, ie2, ie3 ...)

        TODO why do we have this duplicated in IN->EXISTS transformers?
        psergey-todo: fix these: grep for duplicated_subselect_card_check
      */
      if (select_lex->item_list.elements != in_subs->left_expr->cols())
      {
        my_error(ER_OPERAND_COLUMNS, MYF(0), in_subs->left_expr->cols());
        DBUG_RETURN(-1);
      }

      SELECT_LEX *current= thd->lex->current_select;
      thd->lex->current_select= current->return_after_parsing();
      char const *save_where= thd->where;
378
      thd->where= "IN/ALL/ANY subquery";
379 380 381 382 383 384 385 386
        
      bool failure= !in_subs->left_expr->fixed &&
                     in_subs->left_expr->fix_fields(thd, &in_subs->left_expr);
      thd->lex->current_select= current;
      thd->where= save_where;
      if (failure)
        DBUG_RETURN(-1); /* purecov: deadcode */
    }
387

388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410
    DBUG_PRINT("info", ("Checking if subq can be converted to semi-join"));
    /*
      Check if we're in subquery that is a candidate for flattening into a
      semi-join (which is done in flatten_subqueries()). The
      requirements are:
        1. Subquery predicate is an IN/=ANY subq predicate
        2. Subquery is a single SELECT (not a UNION)
        3. Subquery does not have GROUP BY or ORDER BY
        4. Subquery does not use aggregate functions or HAVING
        5. Subquery predicate is at the AND-top-level of ON/WHERE clause
        6. We are not in a subquery of a single table UPDATE/DELETE that 
             doesn't have a JOIN (TODO: We should handle this at some
             point by switching to multi-table UPDATE/DELETE)
        7. We're not in a table-less subquery like "SELECT 1"
        8. No execution method was already chosen (by a prepared statement)
        9. Parent select is not a table-less select
        10. Neither parent nor child select have STRAIGHT_JOIN option.
    */
    if (optimizer_flag(thd, OPTIMIZER_SWITCH_SEMIJOIN) &&
        in_subs &&                                                    // 1
        !select_lex->is_part_of_union() &&                            // 2
        !select_lex->group_list.elements && !join->order &&           // 3
        !join->having && !select_lex->with_sum_func &&                // 4
411
        in_subs->emb_on_expr_nest &&                                  // 5
412
        select_lex->outer_select()->join &&                           // 6
413
        parent_unit->first_select()->leaf_tables.elements &&          // 7
unknown's avatar
unknown committed
414
        !in_subs->has_strategy() &&                                   // 8
415
        select_lex->outer_select()->leaf_tables.elements &&           // 9
416 417 418 419 420 421 422 423
        !((join->select_options |                                     // 10
           select_lex->outer_select()->join->select_options)          // 10
          & SELECT_STRAIGHT_JOIN))                                    // 10
    {
      DBUG_PRINT("info", ("Subquery is semi-join conversion candidate"));

      (void)subquery_types_allow_materialization(in_subs);

424
      in_subs->is_flattenable_semijoin= TRUE;
425 426

      /* Register the subquery for further processing in flatten_subqueries() */
Igor Babaev's avatar
Igor Babaev committed
427 428 429 430 431 432 433 434 435
      if (!in_subs->is_registered_semijoin)
      {
        Query_arena *arena, backup;
        arena= thd->activate_stmt_arena_if_needed(&backup);
        select_lex->outer_select()->sj_subselects.push_back(in_subs);
        if (arena)
          thd->restore_active_arena(arena, &backup);
        in_subs->is_registered_semijoin= TRUE;
      }
436 437 438
    }
    else
    {
Sergey Petrunya's avatar
Sergey Petrunya committed
439
      DBUG_PRINT("info", ("Subquery can't be converted to merged semi-join"));
440
      /* Test if the user has set a legal combination of optimizer switches. */
441 442 443 444
      if (!optimizer_flag(thd, OPTIMIZER_SWITCH_IN_TO_EXISTS) &&
          !optimizer_flag(thd, OPTIMIZER_SWITCH_MATERIALIZATION))
        my_error(ER_ILLEGAL_SUBQUERY_OPTIMIZER_SWITCHES, MYF(0));

445 446 447 448 449
      /*
        If the subquery predicate is IN/=ANY, analyse and set all possible
        subquery execution strategies based on optimizer switches and syntactic
        properties.
      */
450
      if (in_subs && !in_subs->has_strategy())
451
      {
452 453
        if (is_materialization_applicable(thd, in_subs, select_lex))
        {
unknown's avatar
unknown committed
454
          in_subs->add_strategy(SUBS_MATERIALIZATION);
Sergey Petrunya's avatar
Sergey Petrunya committed
455 456 457 458 459

          /*
            If the subquery is an AND-part of WHERE register for being processed
            with jtbm strategy
          */
460
          if (in_subs->emb_on_expr_nest == NO_JOIN_NEST &&
Sergey Petrunya's avatar
Sergey Petrunya committed
461 462 463
              optimizer_flag(thd, OPTIMIZER_SWITCH_SEMIJOIN))
          {
            in_subs->is_flattenable_semijoin= FALSE;
Igor Babaev's avatar
Igor Babaev committed
464 465 466 467 468 469 470 471 472
            if (!in_subs->is_registered_semijoin)
	    {
              Query_arena *arena, backup;
              arena= thd->activate_stmt_arena_if_needed(&backup);
              select_lex->outer_select()->sj_subselects.push_back(in_subs);
              if (arena)
                thd->restore_active_arena(arena, &backup);
              in_subs->is_registered_semijoin= TRUE;
            }
Sergey Petrunya's avatar
Sergey Petrunya committed
473
          }
474
        }
475

476 477 478 479 480 481
        /*
          IN-TO-EXISTS is the only universal strategy. Choose it if the user
          allowed it via an optimizer switch, or if materialization is not
          possible.
        */
        if (optimizer_flag(thd, OPTIMIZER_SWITCH_IN_TO_EXISTS) ||
unknown's avatar
unknown committed
482 483
            !in_subs->has_strategy())
          in_subs->add_strategy(SUBS_IN_TO_EXISTS);
484 485
      }

486
      /* Check if max/min optimization applicable */
unknown's avatar
unknown committed
487 488 489 490 491 492 493
      if (allany_subs && !allany_subs->is_set_strategy())
      {
        uchar strategy= (allany_subs->is_maxmin_applicable(join) ?
                         (SUBS_MAXMIN_INJECTED | SUBS_MAXMIN_ENGINE) :
                         SUBS_IN_TO_EXISTS);
        allany_subs->add_strategy(strategy);
      }
494

495 496 497 498
      /*
        Transform each subquery predicate according to its overloaded
        transformer.
      */
unknown's avatar
unknown committed
499
      if (subselect->select_transformer(join))
500
        DBUG_RETURN(-1);
501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576
    }
  }
  DBUG_RETURN(0);
}


/**
  @brief Check if subquery's compared types allow materialization.

  @param in_subs Subquery predicate, updated as follows:
    types_allow_materialization TRUE if subquery materialization is allowed.
    sjm_scan_allowed            If types_allow_materialization is TRUE,
                                indicates whether it is possible to use subquery
                                materialization and scan the materialized table.

  @retval TRUE   If subquery types allow materialization.
  @retval FALSE  Otherwise.

  @details
    This is a temporary fix for BUG#36752.
    
    There are two subquery materialization strategies:

    1. Materialize and do index lookups in the materialized table. See 
       BUG#36752 for description of restrictions we need to put on the
       compared expressions.

    2. Materialize and then do a full scan of the materialized table. At the
       moment, this strategy's applicability criteria are even stricter than
       in #1.

       This is so because of the following: consider an uncorrelated subquery
       
       ...WHERE (ot1.col1, ot2.col2 ...) IN (SELECT ie1,ie2,... FROM it1 ...)

       and a join order that could be used to do sjm-materialization: 
          
          SJM-Scan(it1, it1), ot1, ot2
       
       IN-equalities will be parts of conditions attached to the outer tables:

         ot1:  ot1.col1 = ie1 AND ... (C1)
         ot2:  ot1.col2 = ie2 AND ... (C2)
       
       besides those there may be additional references to ie1 and ie2
       generated by equality propagation. The problem with evaluating C1 and
       C2 is that ie{1,2} refer to subquery tables' columns, while we only have 
       current value of materialization temptable. Our solution is to 
        * require that all ie{N} are table column references. This allows 
          to copy the values of materialization temptable columns to the
          original table's columns (see setup_sj_materialization for more
          details)
        * require that compared columns have exactly the same type. This is
          a temporary measure to avoid BUG#36752-type problems.
*/

static 
bool subquery_types_allow_materialization(Item_in_subselect *in_subs)
{
  DBUG_ENTER("subquery_types_allow_materialization");

  DBUG_ASSERT(in_subs->left_expr->fixed);

  List_iterator<Item> it(in_subs->unit->first_select()->item_list);
  uint elements= in_subs->unit->first_select()->item_list.elements;

  in_subs->types_allow_materialization= FALSE;  // Assign default values
  in_subs->sjm_scan_allowed= FALSE;
  
  bool all_are_fields= TRUE;
  for (uint i= 0; i < elements; i++)
  {
    Item *outer= in_subs->left_expr->element_index(i);
    Item *inner= it++;
    all_are_fields &= (outer->real_item()->type() == Item::FIELD_ITEM && 
                       inner->real_item()->type() == Item::FIELD_ITEM);
577
    if (outer->cmp_type() != inner->cmp_type())
578
      DBUG_RETURN(FALSE);
579
    switch (outer->cmp_type()) {
580
    case STRING_RESULT:
581
      if (!(outer->collation.collation == inner->collation.collation))
582
        DBUG_RETURN(FALSE);
583 584 585 586
      // Materialization does not work with BLOB columns
      if (inner->field_type() == MYSQL_TYPE_BLOB || 
          inner->field_type() == MYSQL_TYPE_GEOMETRY)
        DBUG_RETURN(FALSE);
587 588 589 590 591 592 593 594 595 596
      /* 
        Materialization also is unable to work when create_tmp_table() will
        create a blob column because item->max_length is too big.
        The following check is copied from Item::make_string_field():
      */ 
      if (inner->max_length / inner->collation.collation->mbmaxlen > 
          CONVERT_IF_BIGGER_TO_BLOB)
      {
        DBUG_RETURN(FALSE);
      }
597 598 599 600
      break;
    case TIME_RESULT:
      if (mysql_type_to_time_type(outer->field_type()) !=
          mysql_type_to_time_type(outer->field_type()))
601 602
        DBUG_RETURN(FALSE);
    default:
603 604
      /* suitable for materialization */
      break;
605 606
    }
  }
607

608 609 610 611 612 613 614
  in_subs->types_allow_materialization= TRUE;
  in_subs->sjm_scan_allowed= all_are_fields;
  DBUG_PRINT("info",("subquery_types_allow_materialization: ok, allowed"));
  DBUG_RETURN(TRUE);
}


615 616 617 618
/**
  Apply max min optimization of all/any subselect
*/

619
bool JOIN::transform_max_min_subquery()
620
{
621 622
  DBUG_ENTER("JOIN::transform_max_min_subquery");
  Item_subselect *subselect= unit->item;
623 624 625
  if (!subselect || (subselect->substype() != Item_subselect::ALL_SUBS &&
                     subselect->substype() != Item_subselect::ANY_SUBS))
    DBUG_RETURN(0);
626 627
  DBUG_RETURN(((Item_allany_subselect *) subselect)->
              transform_into_max_min(this));
628 629 630
}


631 632 633 634 635 636 637 638 639 640 641 642
/*
  Finalize IN->EXISTS conversion in case we couldn't use materialization.

  DESCRIPTION  Invoke the IN->EXISTS converter
    Replace the Item_in_subselect with its wrapper Item_in_optimizer in WHERE.

  RETURN 
    FALSE - Ok
    TRUE  - Fatal error
*/

bool make_in_exists_conversion(THD *thd, JOIN *join, Item_in_subselect *item)
643 644 645
{
  DBUG_ENTER("make_in_exists_conversion");
  JOIN *child_join= item->unit->first_select()->join;
Sergey Petrunya's avatar
Sergey Petrunya committed
646
  bool res;
647 648 649 650 651 652 653 654 655 656 657 658 659 660

  /* 
    We're going to finalize IN->EXISTS conversion. 
    Normally, IN->EXISTS conversion takes place inside the 
    Item_subselect::fix_fields() call, where item_subselect->fixed==FALSE (as
    fix_fields() haven't finished yet) and item_subselect->changed==FALSE (as 
    the conversion haven't been finalized)

    At the end of Item_subselect::fix_fields() we had to set fixed=TRUE,
    changed=TRUE (the only other option would have been to return error).

    So, now we have to set these back for the duration of select_transformer()
    call.
  */
661 662 663 664 665 666 667 668 669 670
  item->changed= 0;
  item->fixed= 0;

  SELECT_LEX *save_select_lex= thd->lex->current_select;
  thd->lex->current_select= item->unit->first_select();

  res= item->select_transformer(child_join);

  thd->lex->current_select= save_select_lex;

Sergey Petrunya's avatar
Sergey Petrunya committed
671
  if (res)
672 673 674 675 676 677 678 679
    DBUG_RETURN(TRUE);

  item->changed= 1;
  item->fixed= 1;

  Item *substitute= item->substitution;
  bool do_fix_fields= !item->substitution->fixed;
  /*
680 681
    The Item_subselect has already been wrapped with Item_in_optimizer, so we
    should search for item->optimizer, not 'item'.
682
  */
683 684
  Item *replace_me= item->optimizer;
  DBUG_ASSERT(replace_me==substitute);
685

686
  Item **tree= (item->emb_on_expr_nest == NO_JOIN_NEST)?
687
                 &join->conds : &(item->emb_on_expr_nest->on_expr);
688 689 690 691 692
  if (replace_where_subcondition(join, tree, replace_me, substitute, 
                                 do_fix_fields))
    DBUG_RETURN(TRUE);
  item->substitution= NULL;
   
693 694 695 696
    /*
      If this is a prepared statement, repeat the above operation for
      prep_where (or prep_on_expr). 
    */
697 698
  if (!thd->stmt_arena->is_conventional())
  {
699
    tree= (item->emb_on_expr_nest == (TABLE_LIST*)NO_JOIN_NEST)?
700 701 702 703 704 705 706 707 708
           &join->select_lex->prep_where : 
           &(item->emb_on_expr_nest->prep_on_expr);

    if (replace_where_subcondition(join, tree, replace_me, substitute, 
                                   FALSE))
      DBUG_RETURN(TRUE);
  }
  DBUG_RETURN(FALSE);
}
709 710


711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730
bool check_for_outer_joins(List<TABLE_LIST> *join_list)
{
  TABLE_LIST *table;
  NESTED_JOIN *nested_join;
  List_iterator<TABLE_LIST> li(*join_list);
  while ((table= li++))
  {
    if ((nested_join= table->nested_join))
    {
      if (check_for_outer_joins(&nested_join->join_list))
        return TRUE;
    }
    
    if (table->outer_join)
      return TRUE;
  }
  return FALSE;
}


731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780
/*
  Convert semi-join subquery predicates into semi-join join nests

  SYNOPSIS
    convert_join_subqueries_to_semijoins()
 
  DESCRIPTION

    Convert candidate subquery predicates into semi-join join nests. This 
    transformation is performed once in query lifetime and is irreversible.
    
    Conversion of one subquery predicate
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    We start with a join that has a semi-join subquery:

      SELECT ...
      FROM ot, ...
      WHERE oe IN (SELECT ie FROM it1 ... itN WHERE subq_where) AND outer_where

    and convert it into a semi-join nest:

      SELECT ...
      FROM ot SEMI JOIN (it1 ... itN), ...
      WHERE outer_where AND subq_where AND oe=ie

    that is, in order to do the conversion, we need to 

     * Create the "SEMI JOIN (it1 .. itN)" part and add it into the parent
       query's FROM structure.
     * Add "AND subq_where AND oe=ie" into parent query's WHERE (or ON if
       the subquery predicate was in an ON expression)
     * Remove the subquery predicate from the parent query's WHERE

    Considerations when converting many predicates
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    A join may have at most MAX_TABLES tables. This may prevent us from
    flattening all subqueries when the total number of tables in parent and
    child selects exceeds MAX_TABLES.
    We deal with this problem by flattening children's subqueries first and
    then using a heuristic rule to determine each subquery predicate's
    "priority".

  RETURN 
    FALSE  OK
    TRUE   Error
*/

bool convert_join_subqueries_to_semijoins(JOIN *join)
{
  Query_arena *arena, backup;
Igor Babaev's avatar
Igor Babaev committed
781
  Item_in_subselect *in_subq;
782
  THD *thd= join->thd;
783
  List_iterator<TABLE_LIST> ti(join->select_lex->leaf_tables);
784 785
  DBUG_ENTER("convert_join_subqueries_to_semijoins");

Igor Babaev's avatar
Igor Babaev committed
786
  if (join->select_lex->sj_subselects.is_empty())
787 788
    DBUG_RETURN(FALSE);

Igor Babaev's avatar
Igor Babaev committed
789 790 791
  List_iterator_fast<Item_in_subselect> li(join->select_lex->sj_subselects);

  while ((in_subq= li++))
792
  {
Igor Babaev's avatar
Igor Babaev committed
793
    SELECT_LEX *subq_sel= in_subq->get_select_lex();
794 795 796 797 798 799 800
    if (subq_sel->handle_derived(thd->lex, DT_OPTIMIZE))
      DBUG_RETURN(1);
    if (subq_sel->handle_derived(thd->lex, DT_MERGE))
      DBUG_RETURN(TRUE);
    subq_sel->update_used_tables();
  }

Igor Babaev's avatar
Igor Babaev committed
801
  li.rewind();
802
  /* First, convert child join's subqueries. We proceed bottom-up here */
Igor Babaev's avatar
Igor Babaev committed
803
  while ((in_subq= li++)) 
804
  {
Igor Babaev's avatar
Igor Babaev committed
805
    st_select_lex *child_select= in_subq->get_select_lex();
806
    JOIN *child_join= child_select->join;
807
    child_join->outer_tables = child_join->table_count;
808 809 810 811 812 813 814 815 816 817 818

    /*
      child_select->where contains only the WHERE predicate of the
      subquery itself here. We may be selecting from a VIEW, which has its
      own predicate. The combined predicates are available in child_join->conds,
      which was built by setup_conds() doing prepare_where() for all views.
    */
    child_select->where= child_join->conds;

    if (convert_join_subqueries_to_semijoins(child_join))
      DBUG_RETURN(TRUE);
Igor Babaev's avatar
Igor Babaev committed
819 820 821
    in_subq->sj_convert_priority= 
      test(in_subq->emb_on_expr_nest != NO_JOIN_NEST) * MAX_TABLES * 2 +
      in_subq->is_correlated * MAX_TABLES + child_join->outer_tables;
822 823 824 825
  }
  
  // Temporary measure: disable semi-joins when they are together with outer
  // joins.
826
#if 0  
827 828
  if (check_for_outer_joins(join->join_list))
  {
Igor Babaev's avatar
Igor Babaev committed
829
    in_subq= join->select_lex->sj_subselects.head();
830 831
    arena= thd->activate_stmt_arena_if_needed(&backup);
    goto skip_conversion;
832
  }
833
#endif
834 835 836 837 838 839 840
  //dump_TABLE_LIST_struct(select_lex, select_lex->leaf_tables);
  /* 
    2. Pick which subqueries to convert:
      sort the subquery array
      - prefer correlated subqueries over uncorrelated;
      - prefer subqueries that have greater number of outer tables;
  */
Igor Babaev's avatar
Igor Babaev committed
841 842
  bubble_sort<Item_in_subselect>(&join->select_lex->sj_subselects,
				 subq_sj_candidate_cmp, NULL);
843 844 845 846
  // #tables-in-parent-query + #tables-in-subquery < MAX_TABLES
  /* Replace all subqueries to be flattened with Item_int(1) */
  arena= thd->activate_stmt_arena_if_needed(&backup);
 
Igor Babaev's avatar
Igor Babaev committed
847 848
  li.rewind();
  while ((in_subq= li++))
849
  {
850
    bool remove_item= TRUE;
851 852

    /* Stop processing if we've reached a subquery that's attached to the ON clause */
Igor Babaev's avatar
Igor Babaev committed
853
    if (in_subq->emb_on_expr_nest != NO_JOIN_NEST)
854 855
      break;

Igor Babaev's avatar
Igor Babaev committed
856
    if (in_subq->is_flattenable_semijoin) 
857
    {
858
      if (join->table_count + 
Igor Babaev's avatar
Igor Babaev committed
859
          in_subq->unit->first_select()->join->table_count >= MAX_TABLES)
860
        break;
Igor Babaev's avatar
Igor Babaev committed
861
      if (convert_subq_to_sj(join, in_subq))
862
        goto restore_arena_and_fail;
863 864 865
    }
    else
    {
866
      if (join->table_count + 1 >= MAX_TABLES)
867
        break;
Igor Babaev's avatar
Igor Babaev committed
868
      if (convert_subq_to_jtbm(join, in_subq, &remove_item))
869
        goto restore_arena_and_fail;
870 871 872
    }
    if (remove_item)
    {
Igor Babaev's avatar
Igor Babaev committed
873 874 875
      Item **tree= (in_subq->emb_on_expr_nest == NO_JOIN_NEST)?
                     &join->conds : &(in_subq->emb_on_expr_nest->on_expr);
      Item *replace_me= in_subq->original_item();
876 877
      if (replace_where_subcondition(join, tree, replace_me, new Item_int(1),
                                     FALSE))
878
        goto restore_arena_and_fail;
879
    }
880
  }
881
//skip_conversion:
882 883 884 885
  /* 
    3. Finalize (perform IN->EXISTS rewrite) the subqueries that we didn't
    convert:
  */
Igor Babaev's avatar
Igor Babaev committed
886
  while (in_subq)
887
  {
Igor Babaev's avatar
Igor Babaev committed
888 889 890
    JOIN *child_join= in_subq->unit->first_select()->join;
    in_subq->changed= 0;
    in_subq->fixed= 0;
891 892

    SELECT_LEX *save_select_lex= thd->lex->current_select;
Igor Babaev's avatar
Igor Babaev committed
893
    thd->lex->current_select= in_subq->unit->first_select();
894

Igor Babaev's avatar
Igor Babaev committed
895
    bool res= in_subq->select_transformer(child_join);
896 897 898

    thd->lex->current_select= save_select_lex;

unknown's avatar
unknown committed
899
    if (res)
900 901
      DBUG_RETURN(TRUE);

Igor Babaev's avatar
Igor Babaev committed
902 903
    in_subq->changed= 1;
    in_subq->fixed= 1;
904

Igor Babaev's avatar
Igor Babaev committed
905 906 907 908 909
    Item *substitute= in_subq->substitution;
    bool do_fix_fields= !in_subq->substitution->fixed;
    Item **tree= (in_subq->emb_on_expr_nest == NO_JOIN_NEST)?
                   &join->conds : &(in_subq->emb_on_expr_nest->on_expr);
    Item *replace_me= in_subq->original_item();
910
    if (replace_where_subcondition(join, tree, replace_me, substitute, 
911 912
                                   do_fix_fields))
      DBUG_RETURN(TRUE);
Igor Babaev's avatar
Igor Babaev committed
913
    in_subq->substitution= NULL;
914 915 916 917 918
    /*
      If this is a prepared statement, repeat the above operation for
      prep_where (or prep_on_expr). Subquery-to-semijoin conversion is 
      done once for prepared statement.
    */
919 920
    if (!thd->stmt_arena->is_conventional())
    {
Igor Babaev's avatar
Igor Babaev committed
921
      tree= (in_subq->emb_on_expr_nest == NO_JOIN_NEST)?
922
             &join->select_lex->prep_where : 
Igor Babaev's avatar
Igor Babaev committed
923
             &(in_subq->emb_on_expr_nest->prep_on_expr);
924 925 926 927 928 929
      /* 
        prep_on_expr/ prep_where may be NULL in some cases. 
        If that is the case, do nothing - simplify_joins() will copy 
        ON/WHERE expression into prep_on_expr/prep_where.
      */
      if (*tree && replace_where_subcondition(join, tree, replace_me, substitute, 
930 931 932
                                     FALSE))
        DBUG_RETURN(TRUE);
    }
933 934
    /*
      Revert to the IN->EXISTS strategy in the rare case when the subquery could
935
      not be flattened.
936
    */
unknown's avatar
unknown committed
937
    in_subq->reset_strategy(SUBS_IN_TO_EXISTS);
938 939 940
    if (is_materialization_applicable(thd, in_subq, 
                                      in_subq->unit->first_select()))
    {
unknown's avatar
unknown committed
941
      in_subq->add_strategy(SUBS_MATERIALIZATION);
942 943
    }

Igor Babaev's avatar
Igor Babaev committed
944
    in_subq= li++;
945 946 947 948
  }

  if (arena)
    thd->restore_active_arena(arena, &backup);
Igor Babaev's avatar
Igor Babaev committed
949
  join->select_lex->sj_subselects.empty();
950
  DBUG_RETURN(FALSE);
951 952 953 954 955

restore_arena_and_fail:
  if (arena)
    thd->restore_active_arena(arena, &backup);
  DBUG_RETURN(TRUE);
956 957
}

958

959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983
/*
  Get #output_rows and scan_time estimates for a "delayed" table.

  SYNOPSIS
    get_delayed_table_estimates()
      table         IN    Table to get estimates for
      out_rows      OUT   E(#rows in the table)
      scan_time     OUT   E(scan_time).
      startup_cost  OUT   cost to populate the table.

  DESCRIPTION
    Get #output_rows and scan_time estimates for a "delayed" table. By
    "delayed" here we mean that the table is filled at the start of query
    execution. This means that the optimizer can't use table statistics to 
    get #rows estimate for it, it has to call this function instead.

    This function is expected to make different actions depending on the nature
    of the table. At the moment there is only one kind of delayed tables,
    non-flattenable semi-joins.
*/

void get_delayed_table_estimates(TABLE *table,
                                 ha_rows *out_rows, 
                                 double *scan_time,
                                 double *startup_cost)
984
{
985
  Item_in_subselect *item= table->pos_in_table_list->jtbm_subselect;
986

987 988 989 990 991
  DBUG_ASSERT(item->engine->engine_type() ==
              subselect_engine::HASH_SJ_ENGINE);

  subselect_hash_sj_engine *hash_sj_engine=
    ((subselect_hash_sj_engine*)item->engine);
992

Sergey Petrunya's avatar
Sergey Petrunya committed
993 994 995
  *out_rows= (ha_rows)item->jtbm_record_count;
  *startup_cost= item->jtbm_read_time;

996
  /* Calculate cost of scanning the temptable */
Sergey Petrunya's avatar
Sergey Petrunya committed
997 998
  double data_size= item->jtbm_record_count * 
                    hash_sj_engine->tmp_table->s->reclength;
999 1000 1001 1002
  /* Do like in handler::read_time */
  *scan_time= data_size/IO_SIZE + 2;
} 

1003

1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020
/**
   @brief Replaces an expression destructively inside the expression tree of
   the WHERE clase.

   @note Because of current requirements for semijoin flattening, we do not
   need to recurse here, hence this function will only examine the top-level
   AND conditions. (see JOIN::prepare, comment starting with "Check if the 
   subquery predicate can be executed via materialization".
   
   @param join The top-level query.
   @param old_cond The expression to be replaced.
   @param new_cond The expression to be substituted.
   @param do_fix_fields If true, Item::fix_fields(THD*, Item**) is called for
   the new expression.
   @return <code>true</code> if there was an error, <code>false</code> if
   successful.
*/
1021

1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048
static bool replace_where_subcondition(JOIN *join, Item **expr, 
                                       Item *old_cond, Item *new_cond,
                                       bool do_fix_fields)
{
  if (*expr == old_cond)
  {
    *expr= new_cond;
    if (do_fix_fields)
      new_cond->fix_fields(join->thd, expr);
    return FALSE;
  }
  
  if ((*expr)->type() == Item::COND_ITEM) 
  {
    List_iterator<Item> li(*((Item_cond*)(*expr))->argument_list());
    Item *item;
    while ((item= li++))
    {
      if (item == old_cond) 
      {
        li.replace(new_cond);
        if (do_fix_fields)
          new_cond->fix_fields(join->thd, li.ref());
        return FALSE;
      }
    }
  }
1049 1050 1051 1052 1053 1054 1055 1056 1057
  /* 
    We can come to here when 
     - we're doing replace operations on both on_expr and prep_on_expr
     - on_expr is the same as prep_on_expr, or they share a sub-tree 
       (so, when we do replace in on_expr, we replace in prep_on_expr, too,
        and when we try doing a replace in prep_on_expr, the item we wanted 
        to replace there has already been replaced)
  */
  return FALSE;
1058 1059
}

Igor Babaev's avatar
Igor Babaev committed
1060 1061
static int subq_sj_candidate_cmp(Item_in_subselect* el1, Item_in_subselect* el2,
                                 void *arg)
1062
{
Igor Babaev's avatar
Igor Babaev committed
1063 1064
  return (el1->sj_convert_priority > el2->sj_convert_priority) ? 1 : 
         ( (el1->sj_convert_priority == el2->sj_convert_priority)? 0 : -1);
1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107
}


/*
  Convert a subquery predicate into a TABLE_LIST semi-join nest

  SYNOPSIS
    convert_subq_to_sj()
       parent_join  Parent join, the one that has subq_pred in its WHERE/ON 
                    clause
       subq_pred    Subquery predicate to be converted
  
  DESCRIPTION
    Convert a subquery predicate into a TABLE_LIST semi-join nest. All the 
    prerequisites are already checked, so the conversion is always successfull.

    Prepared Statements: the transformation is permanent:
     - Changes in TABLE_LIST structures are naturally permanent
     - Item tree changes are performed on statement MEM_ROOT:
        = we activate statement MEM_ROOT 
        = this function is called before the first fix_prepare_information
          call.

    This is intended because the criteria for subquery-to-sj conversion remain
    constant for the lifetime of the Prepared Statement.

  RETURN
    FALSE  OK
    TRUE   Out of memory error
*/

static bool convert_subq_to_sj(JOIN *parent_join, Item_in_subselect *subq_pred)
{
  SELECT_LEX *parent_lex= parent_join->select_lex;
  TABLE_LIST *emb_tbl_nest= NULL;
  List<TABLE_LIST> *emb_join_list= &parent_lex->top_join_list;
  THD *thd= parent_join->thd;
  DBUG_ENTER("convert_subq_to_sj");

  /*
    1. Find out where to put the predicate into.
     Note: for "t1 LEFT JOIN t2" this will be t2, a leaf.
  */
1108
  if ((void*)subq_pred->emb_on_expr_nest != (void*)NO_JOIN_NEST)
1109
  {
1110
    if (subq_pred->emb_on_expr_nest->nested_join)
1111 1112 1113 1114 1115 1116 1117 1118
    {
      /*
        We're dealing with

          ... [LEFT] JOIN  ( ... ) ON (subquery AND whatever) ...

        The sj-nest will be inserted into the brackets nest.
      */
1119
      emb_tbl_nest=  subq_pred->emb_on_expr_nest;
1120 1121
      emb_join_list= &emb_tbl_nest->nested_join->join_list;
    }
1122
    else if (!subq_pred->emb_on_expr_nest->outer_join)
1123 1124 1125 1126 1127 1128 1129 1130 1131
    {
      /*
        We're dealing with

          ... INNER JOIN tblX ON (subquery AND whatever) ...

        The sj-nest will be tblX's "sibling", i.e. another child of its
        parent. This is ok because tblX is joined as an inner join.
      */
1132
      emb_tbl_nest= subq_pred->emb_on_expr_nest->embedding;
1133 1134 1135
      if (emb_tbl_nest)
        emb_join_list= &emb_tbl_nest->nested_join->join_list;
    }
1136
    else if (!subq_pred->emb_on_expr_nest->nested_join)
1137
    {
1138
      TABLE_LIST *outer_tbl= subq_pred->emb_on_expr_nest;
1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229
      TABLE_LIST *wrap_nest;
      /*
        We're dealing with

          ... LEFT JOIN tbl ON (on_expr AND subq_pred) ...

        we'll need to convert it into:

          ... LEFT JOIN ( tbl SJ (subq_tables) ) ON (on_expr AND subq_pred) ...
                        |                      |
                        |<----- wrap_nest ---->|
        
        Q:  other subqueries may be pointing to this element. What to do?
        A1: simple solution: copy *subq_pred->expr_join_nest= *parent_nest.
            But we'll need to fix other pointers.
        A2: Another way: have TABLE_LIST::next_ptr so the following
            subqueries know the table has been nested.
        A3: changes in the TABLE_LIST::outer_join will make everything work
            automatically.
      */
      if (!(wrap_nest= alloc_join_nest(parent_join->thd)))
      {
        DBUG_RETURN(TRUE);
      }
      wrap_nest->embedding= outer_tbl->embedding;
      wrap_nest->join_list= outer_tbl->join_list;
      wrap_nest->alias= (char*) "(sj-wrap)";

      wrap_nest->nested_join->join_list.empty();
      wrap_nest->nested_join->join_list.push_back(outer_tbl);

      outer_tbl->embedding= wrap_nest;
      outer_tbl->join_list= &wrap_nest->nested_join->join_list;

      /*
        wrap_nest will take place of outer_tbl, so move the outer join flag
        and on_expr
      */
      wrap_nest->outer_join= outer_tbl->outer_join;
      outer_tbl->outer_join= 0;

      wrap_nest->on_expr= outer_tbl->on_expr;
      outer_tbl->on_expr= NULL;

      List_iterator<TABLE_LIST> li(*wrap_nest->join_list);
      TABLE_LIST *tbl;
      while ((tbl= li++))
      {
        if (tbl == outer_tbl)
        {
          li.replace(wrap_nest);
          break;
        }
      }
      /*
        Ok now wrap_nest 'contains' outer_tbl and we're ready to add the 
        semi-join nest into it
      */
      emb_join_list= &wrap_nest->nested_join->join_list;
      emb_tbl_nest=  wrap_nest;
    }
  }

  TABLE_LIST *sj_nest;
  NESTED_JOIN *nested_join;
  if (!(sj_nest= alloc_join_nest(parent_join->thd)))
  {
    DBUG_RETURN(TRUE);
  }
  nested_join= sj_nest->nested_join;

  sj_nest->join_list= emb_join_list;
  sj_nest->embedding= emb_tbl_nest;
  sj_nest->alias= (char*) "(sj-nest)";
  sj_nest->sj_subq_pred= subq_pred;
  /* Nests do not participate in those 'chains', so: */
  /* sj_nest->next_leaf= sj_nest->next_local= sj_nest->next_global == NULL*/
  emb_join_list->push_back(sj_nest);

  /* 
    nested_join->used_tables and nested_join->not_null_tables are
    initialized in simplify_joins().
  */
  
  /* 
    2. Walk through subquery's top list and set 'embedding' to point to the
       sj-nest.
  */
  st_select_lex *subq_lex= subq_pred->unit->first_select();
  nested_join->join_list.empty();
  List_iterator_fast<TABLE_LIST> li(subq_lex->top_join_list);
1230
  TABLE_LIST *tl;
1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244
  while ((tl= li++))
  {
    tl->embedding= sj_nest;
    tl->join_list= &nested_join->join_list;
    nested_join->join_list.push_back(tl);
  }
  
  /*
    Reconnect the next_leaf chain.
    TODO: Do we have to put subquery's tables at the end of the chain?
          Inserting them at the beginning would be a bit faster.
    NOTE: We actually insert them at the front! That's because the order is
          reversed in this list.
  */
1245
  parent_lex->leaf_tables.concat(&subq_lex->leaf_tables);
1246 1247 1248 1249 1250 1251

  /*
    Same as above for next_local chain
    (a theory: a next_local chain always starts with ::leaf_tables
     because view's tables are inserted after the view)
  */
1252 1253
  for (tl= parent_lex->leaf_tables.head(); tl->next_local; tl= tl->next_local) ;
  tl->next_local= subq_lex->leaf_tables.head();
1254 1255 1256 1257 1258 1259

  /* A theory: no need to re-connect the next_global chain */

  /* 3. Remove the original subquery predicate from the WHERE/ON */

  // The subqueries were replaced for Item_int(1) earlier
unknown's avatar
unknown committed
1260
  subq_pred->reset_strategy(SUBS_SEMI_JOIN);       // for subsequent executions
1261 1262
  /*TODO: also reset the 'with_subselect' there. */

1263 1264
  /* n. Adjust the parent_join->table_count counter */
  uint table_no= parent_join->table_count;
1265
  /* n. Walk through child's tables and adjust table->map */
1266 1267
  List_iterator_fast<TABLE_LIST> si(subq_lex->leaf_tables);
  while ((tl= si++))
1268 1269 1270
  {
    tl->table->tablenr= table_no;
    tl->table->map= ((table_map)1) << table_no;
1271
    if (tl->is_jtbm())
1272
      tl->jtbm_table_no= tl->table->tablenr;
1273 1274 1275 1276 1277 1278
    SELECT_LEX *old_sl= tl->select_lex;
    tl->select_lex= parent_join->select_lex; 
    for (TABLE_LIST *emb= tl->embedding;
         emb && emb->select_lex == old_sl;
         emb= emb->embedding)
      emb->select_lex= parent_join->select_lex;
1279
    table_no++;
1280
  }
1281
  parent_join->table_count += subq_lex->join->table_count;
Sergey Petrunya's avatar
Sergey Petrunya committed
1282
  //parent_join->table_count += subq_lex->leaf_tables.elements;
1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297

  /* 
    Put the subquery's WHERE into semi-join's sj_on_expr
    Add the subquery-induced equalities too.
  */
  SELECT_LEX *save_lex= thd->lex->current_select;
  thd->lex->current_select=subq_lex;
  if (!subq_pred->left_expr->fixed &&
       subq_pred->left_expr->fix_fields(thd, &subq_pred->left_expr))
    DBUG_RETURN(TRUE);
  thd->lex->current_select=save_lex;

  sj_nest->nested_join->sj_corr_tables= subq_pred->used_tables();
  sj_nest->nested_join->sj_depends_on=  subq_pred->used_tables() |
                                        subq_pred->left_expr->used_tables();
1298
  sj_nest->sj_on_expr= subq_lex->join->conds;
1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339

  /*
    Create the IN-equalities and inject them into semi-join's ON expression.
    Additionally, for LooseScan strategy
     - Record the number of IN-equalities.
     - Create list of pointers to (oe1, ..., ieN). We'll need the list to
       see which of the expressions are bound and which are not (for those
       we'll produce a distinct stream of (ie_i1,...ie_ik).

       (TODO: can we just create a list of pointers and hope the expressions
       will not substitute themselves on fix_fields()? or we need to wrap
       them into Item_direct_view_refs and store pointers to those. The
       pointers to Item_direct_view_refs are guaranteed to be stable as 
       Item_direct_view_refs doesn't substitute itself with anything in 
       Item_direct_view_ref::fix_fields.
  */
  sj_nest->sj_in_exprs= subq_pred->left_expr->cols();
  sj_nest->nested_join->sj_outer_expr_list.empty();

  if (subq_pred->left_expr->cols() == 1)
  {
    nested_join->sj_outer_expr_list.push_back(subq_pred->left_expr);
    Item_func_eq *item_eq=
      new Item_func_eq(subq_pred->left_expr, subq_lex->ref_pointer_array[0]);
    item_eq->in_equality_no= 0;
    sj_nest->sj_on_expr= and_items(sj_nest->sj_on_expr, item_eq);
  }
  else
  {
    for (uint i= 0; i < subq_pred->left_expr->cols(); i++)
    {
      nested_join->sj_outer_expr_list.push_back(subq_pred->left_expr->
                                                element_index(i));
      Item_func_eq *item_eq= 
        new Item_func_eq(subq_pred->left_expr->element_index(i), 
                         subq_lex->ref_pointer_array[i]);
      item_eq->in_equality_no= i;
      sj_nest->sj_on_expr= and_items(sj_nest->sj_on_expr, item_eq);
    }
  }
  /* Fix the created equality and AND */
Igor Babaev's avatar
Igor Babaev committed
1340 1341
  if (!sj_nest->sj_on_expr->fixed)
    sj_nest->sj_on_expr->fix_fields(parent_join->thd, &sj_nest->sj_on_expr);
1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361

  /*
    Walk through sj nest's WHERE and ON expressions and call
    item->fix_table_changes() for all items.
  */
  sj_nest->sj_on_expr->fix_after_pullout(parent_lex, &sj_nest->sj_on_expr);
  fix_list_after_tbl_changes(parent_lex, &sj_nest->nested_join->join_list);


  /* Unlink the child select_lex so it doesn't show up in EXPLAIN: */
  subq_lex->master_unit()->exclude_level();

  DBUG_EXECUTE("where",
               print_where(sj_nest->sj_on_expr,"SJ-EXPR", QT_ORDINARY););

  /* Inject sj_on_expr into the parent's WHERE or ON */
  if (emb_tbl_nest)
  {
    emb_tbl_nest->on_expr= and_items(emb_tbl_nest->on_expr, 
                                     sj_nest->sj_on_expr);
1362
    emb_tbl_nest->on_expr->top_level_item();
Igor Babaev's avatar
Igor Babaev committed
1363 1364 1365
    if (!emb_tbl_nest->on_expr->fixed)
      emb_tbl_nest->on_expr->fix_fields(parent_join->thd,
                                        &emb_tbl_nest->on_expr);
1366 1367 1368 1369 1370
  }
  else
  {
    /* Inject into the WHERE */
    parent_join->conds= and_items(parent_join->conds, sj_nest->sj_on_expr);
1371
    parent_join->conds->top_level_item();
unknown's avatar
unknown committed
1372 1373 1374 1375
    /*
      fix_fields must update the properties (e.g. st_select_lex::cond_count of
      the correct select_lex.
    */
unknown's avatar
unknown committed
1376 1377
    save_lex= thd->lex->current_select;
    thd->lex->current_select=parent_join->select_lex;
Igor Babaev's avatar
Igor Babaev committed
1378 1379
    if (!parent_join->conds->fixed)
      parent_join->conds->fix_fields(parent_join->thd, &parent_join->conds);
unknown's avatar
unknown committed
1380
    thd->lex->current_select=save_lex;
1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394
    parent_join->select_lex->where= parent_join->conds;
  }

  if (subq_lex->ftfunc_list->elements)
  {
    Item_func_match *ifm;
    List_iterator_fast<Item_func_match> li(*(subq_lex->ftfunc_list));
    while ((ifm= li++))
      parent_lex->ftfunc_list->push_front(ifm);
  }

  DBUG_RETURN(FALSE);
}

1395

1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406
const int SUBQERY_TEMPTABLE_NAME_MAX_LEN= 20;

static void create_subquery_temptable_name(char *to, uint number)
{
  DBUG_ASSERT(number < 10000);       
  to= strmov(to, "<subquery");
  to= int10_to_str((int) number, to, 10);
  to[0]= '>';
  to[1]= 0;
}

1407

Sergey Petrunya's avatar
Sergey Petrunya committed
1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421
/*
  Convert subquery predicate into non-mergeable semi-join nest.

  TODO: 
    why does this do IN-EXISTS conversion? Can't we unify it with mergeable
    semi-joins? currently, convert_subq_to_sj() cannot fail to convert (unless
    fatal errors)

    
  RETURN 
    FALSE - Ok
    TRUE  - Fatal error
*/

1422 1423 1424 1425 1426 1427 1428
static bool convert_subq_to_jtbm(JOIN *parent_join, 
                                 Item_in_subselect *subq_pred, 
                                 bool *remove_item)
{
  SELECT_LEX *parent_lex= parent_join->select_lex;
  List<TABLE_LIST> *emb_join_list= &parent_lex->top_join_list;
  TABLE_LIST *emb_tbl_nest= NULL; // will change when we learn to handle outer joins
1429
  TABLE_LIST *tl;
Sergey Petrunya's avatar
Sergey Petrunya committed
1430 1431
  double rows;
  double read_time;
Sergey Petrunya's avatar
Sergey Petrunya committed
1432
  DBUG_ENTER("convert_subq_to_jtbm");
Sergey Petrunya's avatar
Sergey Petrunya committed
1433

unknown's avatar
unknown committed
1434
  subq_pred->set_strategy(SUBS_MATERIALIZATION);
1435 1436
  if (subq_pred->optimize(&rows, &read_time))
    DBUG_RETURN(TRUE);
Sergey Petrunya's avatar
Sergey Petrunya committed
1437 1438 1439 1440 1441

  subq_pred->jtbm_read_time= read_time;
  subq_pred->jtbm_record_count=rows;
  subq_pred->is_jtbm_merged= TRUE;

1442 1443 1444
  if (subq_pred->engine->engine_type() != subselect_engine::HASH_SJ_ENGINE)
  {
    *remove_item= FALSE;
Sergey Petrunya's avatar
Sergey Petrunya committed
1445
    DBUG_RETURN(FALSE);
1446
  }
Sergey Petrunya's avatar
Sergey Petrunya committed
1447 1448


1449 1450 1451 1452
  *remove_item= TRUE;

  TABLE_LIST *jtbm;
  char *tbl_alias;
1453
  if (!(tbl_alias= (char*)parent_join->thd->calloc(SUBQERY_TEMPTABLE_NAME_MAX_LEN)) ||
1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468
      !(jtbm= alloc_join_nest(parent_join->thd))) //todo: this is not a join nest!
  {
    DBUG_RETURN(TRUE);
  }

  jtbm->join_list= emb_join_list;
  jtbm->embedding= emb_tbl_nest;
  jtbm->jtbm_subselect= subq_pred;
  jtbm->nested_join= NULL;

  /* Nests do not participate in those 'chains', so: */
  /* jtbm->next_leaf= jtbm->next_local= jtbm->next_global == NULL*/
  emb_join_list->push_back(jtbm);
  
  /* 
Sergey Petrunya's avatar
Sergey Petrunya committed
1469 1470
    Inject the jtbm table into TABLE_LIST::next_leaf list, so that 
    make_join_statistics() and co. can find it.
1471
  */
1472
  parent_lex->leaf_tables.push_back(jtbm);
1473 1474

  /*
Sergey Petrunya's avatar
Sergey Petrunya committed
1475
    Same as above for TABLE_LIST::next_local chain
1476 1477 1478
    (a theory: a next_local chain always starts with ::leaf_tables
     because view's tables are inserted after the view)
  */
1479
  for (tl= parent_lex->leaf_tables.head(); tl->next_local; tl= tl->next_local)
1480
  {}
1481 1482 1483 1484 1485 1486 1487 1488
  tl->next_local= jtbm;

  /* A theory: no need to re-connect the next_global chain */

  subselect_hash_sj_engine *hash_sj_engine=
    ((subselect_hash_sj_engine*)subq_pred->engine);
  jtbm->table= hash_sj_engine->tmp_table;

1489 1490
  jtbm->table->tablenr= parent_join->table_count;
  jtbm->table->map= table_map(1) << (parent_join->table_count);
1491
  jtbm->jtbm_table_no= jtbm->table->tablenr;
1492

1493 1494
  parent_join->table_count++;
  DBUG_ASSERT(parent_join->table_count < MAX_TABLES);
1495 1496 1497 1498 1499 1500

  Item *conds= hash_sj_engine->semi_join_conds;
  conds->fix_after_pullout(parent_lex, &conds);

  DBUG_EXECUTE("where", print_where(conds,"SJ-EXPR", QT_ORDINARY););
  
1501 1502 1503
  create_subquery_temptable_name(tbl_alias, hash_sj_engine->materialize_join->
                                              select_lex->select_number);
  jtbm->alias= tbl_alias;
1504
#if 0
1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520
  /* Inject sj_on_expr into the parent's WHERE or ON */
  if (emb_tbl_nest)
  {
    DBUG_ASSERT(0);
    /*emb_tbl_nest->on_expr= and_items(emb_tbl_nest->on_expr, 
                                     sj_nest->sj_on_expr);
    emb_tbl_nest->on_expr->fix_fields(parent_join->thd, &emb_tbl_nest->on_expr);
    */
  }
  else
  {
    /* Inject into the WHERE */
    parent_join->conds= and_items(parent_join->conds, conds);
    parent_join->conds->fix_fields(parent_join->thd, &parent_join->conds);
    parent_join->select_lex->where= parent_join->conds;
  }
1521
#endif
1522
  /* Don't unlink the child subselect, as the subquery will be used. */
1523 1524 1525 1526 1527

  DBUG_RETURN(FALSE);
}


1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553
static TABLE_LIST *alloc_join_nest(THD *thd)
{
  TABLE_LIST *tbl;
  if (!(tbl= (TABLE_LIST*) thd->calloc(ALIGN_SIZE(sizeof(TABLE_LIST))+
                                       sizeof(NESTED_JOIN))))
    return NULL;
  tbl->nested_join= (NESTED_JOIN*) ((uchar*)tbl + 
                                    ALIGN_SIZE(sizeof(TABLE_LIST)));
  return tbl;
}


void fix_list_after_tbl_changes(SELECT_LEX *new_parent, List<TABLE_LIST> *tlist)
{
  List_iterator<TABLE_LIST> it(*tlist);
  TABLE_LIST *table;
  while ((table= it++))
  {
    if (table->on_expr)
      table->on_expr->fix_after_pullout(new_parent, &table->on_expr);
    if (table->nested_join)
      fix_list_after_tbl_changes(new_parent, &table->nested_join->join_list);
  }
}


1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572
static void set_emb_join_nest(List<TABLE_LIST> *tables, TABLE_LIST *emb_sj_nest)
{
  List_iterator<TABLE_LIST> it(*tables);
  TABLE_LIST *tbl;
  while ((tbl= it++))
  {
    /*
      Note: check for nested_join first. 
       derived-merged tables have tbl->table!=NULL &&
       tbl->table->reginfo==NULL.
    */
    if (tbl->nested_join)
      set_emb_join_nest(&tbl->nested_join->join_list, emb_sj_nest);
    else if (tbl->table)
      tbl->table->reginfo.join_tab->emb_sj_nest= emb_sj_nest;

  }
}

1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629
/*
  Pull tables out of semi-join nests, if possible

  SYNOPSIS
    pull_out_semijoin_tables()
      join  The join where to do the semi-join flattening

  DESCRIPTION
    Try to pull tables out of semi-join nests.
     
    PRECONDITIONS
    When this function is called, the join may have several semi-join nests
    but it is guaranteed that one semi-join nest does not contain another.
   
    ACTION
    A table can be pulled out of the semi-join nest if
     - It is a constant table, or
     - It is accessed via eq_ref(outer_tables)

    POSTCONDITIONS
     * Tables that were pulled out have JOIN_TAB::emb_sj_nest == NULL
     * Tables that were not pulled out have JOIN_TAB::emb_sj_nest pointing 
       to semi-join nest they are in.
     * Semi-join nests' TABLE_LIST::sj_inner_tables is updated accordingly

    This operation is (and should be) performed at each PS execution since
    tables may become/cease to be constant across PS reexecutions.
    
  NOTE
    Table pullout may make uncorrelated subquery correlated. Consider this
    example:
    
     ... WHERE oe IN (SELECT it1.primary_key WHERE p(it1, it2) ... ) 
    
    here table it1 can be pulled out (we have it1.primary_key=oe which gives
    us functional dependency). Once it1 is pulled out, all references to it1
    from p(it1, it2) become references to outside of the subquery and thus
    make the subquery (i.e. its semi-join nest) correlated.
    Making the subquery (i.e. its semi-join nest) correlated prevents us from
    using Materialization or LooseScan to execute it. 

  RETURN 
    0 - OK
    1 - Out of memory error
*/

int pull_out_semijoin_tables(JOIN *join)
{
  TABLE_LIST *sj_nest;
  DBUG_ENTER("pull_out_semijoin_tables");
  List_iterator<TABLE_LIST> sj_list_it(join->select_lex->sj_nests);
   
  /* Try pulling out of the each of the semi-joins */
  while ((sj_nest= sj_list_it++))
  {
    List_iterator<TABLE_LIST> child_li(sj_nest->nested_join->join_list);
    TABLE_LIST *tbl;
1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655

    /*
      Don't do table pull-out for nested joins (if we get nested joins here, it
      means these are outer joins. It is theoretically possible to do pull-out
      for some of the outer tables but we dont support this currently.
    */
    bool have_join_nest_children= FALSE;

    set_emb_join_nest(&sj_nest->nested_join->join_list, sj_nest);

    while ((tbl= child_li++))
    {
      if (tbl->nested_join)
      {
        have_join_nest_children= TRUE;
        break;
      }
    }
    
    
    table_map pulled_tables= 0;
    if (have_join_nest_children)
      goto skip;

    /* Action #1: Mark the constant tables to be pulled out */
    child_li.rewind();
1656 1657 1658 1659 1660
    while ((tbl= child_li++))
    {
      if (tbl->table)
      {
        tbl->table->reginfo.join_tab->emb_sj_nest= sj_nest;
1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681
#if 0 
        /* 
          Do not pull out tables because they are constant. This operation has
          a problem:
          - Some constant tables may become/cease to be constant across PS
            re-executions
          - Contrary to our initial assumption, it turned out that table pullout 
            operation is not easily undoable.

          The solution is to leave constant tables where they are. This will
          affect only constant tables that are 1-row or empty, tables that are
          constant because they are accessed via eq_ref(const) access will
          still be pulled out as functionally-dependent.

          This will cause us to miss the chance to flatten some of the 
          subqueries, but since const tables do not generate many duplicates,
          it really doesn't matter that much whether they were pulled out or
          not.

          All of this was done as fix for BUG#43768.
        */
1682 1683 1684 1685 1686 1687
        if (tbl->table->map & join->const_table_map)
        {
          pulled_tables |= tbl->table->map;
          DBUG_PRINT("info", ("Table %s pulled out (reason: constant)",
                              tbl->table->alias));
        }
1688
#endif
1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712
      }
    }
    
    /*
      Action #2: Find which tables we can pull out based on
      update_ref_and_keys() data. Note that pulling one table out can allow
      us to pull out some other tables too.
    */
    bool pulled_a_table;
    do 
    {
      pulled_a_table= FALSE;
      child_li.rewind();
      while ((tbl= child_li++))
      {
        if (tbl->table && !(pulled_tables & tbl->table->map))
        {
          if (find_eq_ref_candidate(tbl->table, 
                                    sj_nest->nested_join->used_tables & 
                                    ~pulled_tables))
          {
            pulled_a_table= TRUE;
            pulled_tables |= tbl->table->map;
            DBUG_PRINT("info", ("Table %s pulled out (reason: func dep)",
1713
                                tbl->table->alias.c_ptr()));
1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726
            /*
              Pulling a table out of uncorrelated subquery in general makes
              makes it correlated. See the NOTE to this funtion. 
            */
            sj_nest->sj_subq_pred->is_correlated= TRUE;
            sj_nest->nested_join->sj_corr_tables|= tbl->table->map;
            sj_nest->nested_join->sj_depends_on|= tbl->table->map;
          }
        }
      }
    } while (pulled_a_table);
 
    child_li.rewind();
1727
  skip:
1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760
    /*
      Action #3: Move the pulled out TABLE_LIST elements to the parents.
    */
    table_map inner_tables= sj_nest->nested_join->used_tables & 
                            ~pulled_tables;
    /* Record the bitmap of inner tables */
    sj_nest->sj_inner_tables= inner_tables;
    if (pulled_tables)
    {
      List<TABLE_LIST> *upper_join_list= (sj_nest->embedding != NULL)?
                                           (&sj_nest->embedding->nested_join->join_list): 
                                           (&join->select_lex->top_join_list);
      Query_arena *arena, backup;
      arena= join->thd->activate_stmt_arena_if_needed(&backup);
      while ((tbl= child_li++))
      {
        if (tbl->table)
        {
          if (inner_tables & tbl->table->map)
          {
            /* This table is not pulled out */
            tbl->table->reginfo.join_tab->emb_sj_nest= sj_nest;
          }
          else
          {
            /* This table has been pulled out of the semi-join nest */
            tbl->table->reginfo.join_tab->emb_sj_nest= NULL;
            /*
              Pull the table up in the same way as simplify_joins() does:
              update join_list and embedding pointers but keep next[_local]
              pointers.
            */
            child_li.remove();
1761
            sj_nest->nested_join->used_tables &= ~tbl->table->map;
1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806
            upper_join_list->push_back(tbl);
            tbl->join_list= upper_join_list;
            tbl->embedding= sj_nest->embedding;
          }
        }
      }

      /* Remove the sj-nest itself if we've removed everything from it */
      if (!inner_tables)
      {
        List_iterator<TABLE_LIST> li(*upper_join_list);
        /* Find the sj_nest in the list. */
        while (sj_nest != li++) ;
        li.remove();
        /* Also remove it from the list of SJ-nests: */
        sj_list_it.remove();
      }

      if (arena)
        join->thd->restore_active_arena(arena, &backup);
    }
  }
  DBUG_RETURN(0);
}


/* 
  Optimize semi-join nests that could be run with sj-materialization

  SYNOPSIS
    optimize_semijoin_nests()
      join           The join to optimize semi-join nests for
      all_table_map  Bitmap of all tables in the join

  DESCRIPTION
    Optimize each of the semi-join nests that can be run with
    materialization. For each of the nests, we
     - Generate the best join order for this "sub-join" and remember it;
     - Remember the sub-join execution cost (it's part of materialization
       cost);
     - Calculate other costs that will be incurred if we decide 
       to use materialization strategy for this semi-join nest.

    All obtained information is saved and will be used by the main join
    optimization pass.
1807 1808 1809
  
  NOTES 
    Because of Join::reoptimize(), this function may be called multiple times.
1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820

  RETURN
    FALSE  Ok 
    TRUE   Out of memory error
*/

bool optimize_semijoin_nests(JOIN *join, table_map all_table_map)
{
  DBUG_ENTER("optimize_semijoin_nests");
  List_iterator<TABLE_LIST> sj_list_it(join->select_lex->sj_nests);
  TABLE_LIST *sj_nest;
1821
  while ((sj_nest= sj_list_it++))
1822
  {
1823 1824
    /* semi-join nests with only constant tables are not valid */
   /// DBUG_ASSERT(sj_nest->sj_inner_tables & ~join->const_table_map);
1825

1826 1827 1828 1829 1830 1831 1832 1833 1834
    sj_nest->sj_mat_info= NULL;
    /*
      The statement may have been executed with 'semijoin=on' earlier.
      We need to verify that 'semijoin=on' still holds.
     */
    if (optimizer_flag(join->thd, OPTIMIZER_SWITCH_SEMIJOIN) &&
        optimizer_flag(join->thd, OPTIMIZER_SWITCH_MATERIALIZATION))
    {
      if ((sj_nest->sj_inner_tables  & ~join->const_table_map) && /* not everything was pulled out */
1835 1836 1837 1838
          !sj_nest->sj_subq_pred->is_correlated && 
           sj_nest->sj_subq_pred->types_allow_materialization)
      {
        join->emb_sjm_nest= sj_nest;
1839
        if (choose_plan(join, all_table_map &~join->const_table_map))
1840 1841 1842 1843 1844
          DBUG_RETURN(TRUE); /* purecov: inspected */
        /*
          The best plan to run the subquery is now in join->best_positions,
          save it.
        */
1845
        uint n_tables= my_count_bits(sj_nest->sj_inner_tables & ~join->const_table_map);
1846 1847 1848 1849 1850 1851 1852 1853
        SJ_MATERIALIZATION_INFO* sjm;
        if (!(sjm= new SJ_MATERIALIZATION_INFO) ||
            !(sjm->positions= (POSITION*)join->thd->alloc(sizeof(POSITION)*
                                                          n_tables)))
          DBUG_RETURN(TRUE); /* purecov: inspected */
        sjm->tables= n_tables;
        sjm->is_used= FALSE;
        double subjoin_out_rows, subjoin_read_time;
Sergey Petrunya's avatar
Sergey Petrunya committed
1854 1855

        /*
Sergey Petrunya's avatar
Sergey Petrunya committed
1856 1857 1858 1859
        join->get_partial_cost_and_fanout(n_tables + join->const_tables,
                                          table_map(-1),
                                          &subjoin_read_time, 
                                          &subjoin_out_rows);
Sergey Petrunya's avatar
Sergey Petrunya committed
1860 1861 1862 1863
        */
        join->get_prefix_cost_and_fanout(n_tables, 
                                         &subjoin_read_time,
                                         &subjoin_out_rows);
1864 1865 1866

        sjm->materialization_cost.convert_from_cost(subjoin_read_time);
        sjm->rows= subjoin_out_rows;
1867 1868 1869 1870 1871 1872
        
        // Don't use the following list because it has "stale" items. use
        // ref_pointer_array instead:
        //
        //List<Item> &right_expr_list= 
        //  sj_nest->sj_subq_pred->unit->first_select()->item_list;
1873 1874 1875 1876 1877 1878 1879 1880 1881 1882 1883 1884 1885 1886
        /*
          Adjust output cardinality estimates. If the subquery has form

           ... oe IN (SELECT t1.colX, t2.colY, func(X,Y,Z) )

           then the number of distinct output record combinations has an
           upper bound of product of number of records matching the tables 
           that are used by the SELECT clause.
           TODO:
             We can get a more precise estimate if we
              - use rec_per_key cardinality estimates. For simple cases like 
                "oe IN (SELECT t.key ...)" it is trivial. 
              - Functional dependencies between the tables in the semi-join
                nest (the payoff is probably less here?)
1887 1888
          
          See also get_post_group_estimate().
1889
        */
1890
        SELECT_LEX *subq_select= sj_nest->sj_subq_pred->unit->first_select();
1891 1892 1893 1894 1895 1896
        {
          for (uint i=0 ; i < join->const_tables + sjm->tables ; i++)
          {
            JOIN_TAB *tab= join->best_positions[i].table;
            join->map2table[tab->table->tablenr]= tab;
          }
1897 1898 1899
          //List_iterator<Item> it(right_expr_list);
          Item **ref_array= subq_select->ref_pointer_array;
          Item **ref_array_end= ref_array + subq_select->item_list.elements; 
1900
          table_map map= 0;
1901 1902 1903
          //while ((item= it++))
          for (;ref_array < ref_array_end; ref_array++)
            map |= (*ref_array)->used_tables();
1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917
          map= map & ~PSEUDO_TABLE_BITS;
          Table_map_iterator tm_it(map);
          int tableno;
          double rows= 1.0;
          while ((tableno = tm_it.next_bit()) != Table_map_iterator::BITMAP_END)
            rows *= join->map2table[tableno]->table->quick_condition_rows;
          sjm->rows= min(sjm->rows, rows);
        }
        memcpy(sjm->positions, join->best_positions + join->const_tables, 
               sizeof(POSITION) * n_tables);

        /*
          Calculate temporary table parameters and usage costs
        */
1918 1919
        uint rowlen= get_tmp_table_rec_length(subq_select->ref_pointer_array,
                                              subq_select->item_list.elements);
unknown's avatar
unknown committed
1920 1921 1922 1923
        double lookup_cost= get_tmp_table_lookup_cost(join->thd,
                                                      subjoin_out_rows, rowlen);
        double write_cost= get_tmp_table_write_cost(join->thd,
                                                    subjoin_out_rows, rowlen);
1924 1925 1926 1927 1928

        /*
          Let materialization cost include the cost to write the data into the
          temporary table:
        */ 
unknown's avatar
unknown committed
1929
        sjm->materialization_cost.add_io(subjoin_out_rows, write_cost);
1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947
        
        /*
          Set the cost to do a full scan of the temptable (will need this to 
          consider doing sjm-scan):
        */ 
        sjm->scan_cost.zero();
        sjm->scan_cost.add_io(sjm->rows, lookup_cost);

        sjm->lookup_cost.convert_from_cost(lookup_cost);
        sj_nest->sj_mat_info= sjm;
        DBUG_EXECUTE("opt", print_sjm(sjm););
      }
    }
  }
  join->emb_sjm_nest= NULL;
  DBUG_RETURN(FALSE);
}

1948

1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965
/*
  Get estimated record length for semi-join materialization temptable
  
  SYNOPSIS
    get_tmp_table_rec_length()
      items  IN subquery's select list.

  DESCRIPTION
    Calculate estimated record length for semi-join materialization
    temptable. It's an estimate because we don't follow every bit of
    create_tmp_table()'s logic. This isn't necessary as the return value of
    this function is used only for cost calculations.

  RETURN
    Length of the temptable record, in bytes
*/

1966
static uint get_tmp_table_rec_length(Item **p_items, uint elements)
1967 1968 1969
{
  uint len= 0;
  Item *item;
1970 1971 1972
  //List_iterator<Item> it(items);
  Item **p_item;
  for (p_item= p_items; p_item < p_items + elements ; p_item++)
1973
  {
1974
    item = *p_item;
1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
    switch (item->result_type()) {
    case REAL_RESULT:
      len += sizeof(double);
      break;
    case INT_RESULT:
      if (item->max_length >= (MY_INT32_NUM_DECIMAL_DIGITS - 1))
        len += 8;
      else
        len += 4;
      break;
    case STRING_RESULT:
      enum enum_field_types type;
      /* DATE/TIME and GEOMETRY fields have STRING_RESULT result type.  */
      if ((type= item->field_type()) == MYSQL_TYPE_DATETIME ||
          type == MYSQL_TYPE_TIME || type == MYSQL_TYPE_DATE ||
          type == MYSQL_TYPE_TIMESTAMP || type == MYSQL_TYPE_GEOMETRY)
        len += 8;
      else
        len += item->max_length;
      break;
    case DECIMAL_RESULT:
      len += 10;
      break;
    case ROW_RESULT:
    default:
      DBUG_ASSERT(0); /* purecov: deadcode */
      break;
    }
  }
  return len;
}

unknown's avatar
unknown committed
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018

/**
  The cost of a lookup into a unique hash/btree index on a temporary table
  with 'row_count' rows each of size 'row_size'.

  @param thd  current query context
  @param row_count  number of rows in the temp table
  @param row_size   average size in bytes of the rows

  @return  the cost of one lookup
*/

unknown's avatar
unknown committed
2019 2020
static double
get_tmp_table_lookup_cost(THD *thd, double row_count, uint row_size)
unknown's avatar
unknown committed
2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038
{
  if (row_count * row_size > thd->variables.max_heap_table_size)
    return (double) DISK_TEMPTABLE_LOOKUP_COST;
  else
    return (double) HEAP_TEMPTABLE_LOOKUP_COST;
}

/**
  The cost of writing a row into a temporary table with 'row_count' unique
  rows each of size 'row_size'.

  @param thd  current query context
  @param row_count  number of rows in the temp table
  @param row_size   average size in bytes of the rows

  @return  the cost of writing one row
*/

unknown's avatar
unknown committed
2039 2040
static double
get_tmp_table_write_cost(THD *thd, double row_count, uint row_size)
unknown's avatar
unknown committed
2041 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051
{
  double lookup_cost= get_tmp_table_lookup_cost(thd, row_count, row_size);
  /*
    TODO:
    This is an optimistic estimate. Add additional costs resulting from
    actually writing the row to memory/disk and possible index reorganization.
  */
  return lookup_cost;
}


2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064 2065 2066 2067
/*
  Check if table's KEYUSE elements have an eq_ref(outer_tables) candidate

  SYNOPSIS
    find_eq_ref_candidate()
      table             Table to be checked
      sj_inner_tables   Bitmap of inner tables. eq_ref(inner_table) doesn't
                        count.

  DESCRIPTION
    Check if table's KEYUSE elements have an eq_ref(outer_tables) candidate

  TODO
    Check again if it is feasible to factor common parts with constant table
    search

Sergey Petrunya's avatar
Sergey Petrunya committed
2068 2069
    Also check if it's feasible to factor common parts with table elimination

2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080
  RETURN
    TRUE  - There exists an eq_ref(outer-tables) candidate
    FALSE - Otherwise
*/

bool find_eq_ref_candidate(TABLE *table, table_map sj_inner_tables)
{
  KEYUSE *keyuse= table->reginfo.join_tab->keyuse;

  if (keyuse)
  {
2081
    do
2082
    {
2083
      uint key= keyuse->key;
2084
      KEY *keyinfo;
2085
      key_part_map bound_parts= 0;
2086 2087 2088 2089 2090 2091 2092
      bool is_excluded_key= keyuse->is_for_hash_join(); 
      if (!is_excluded_key)
      {
        keyinfo= table->key_info + key;
        is_excluded_key= !test(keyinfo->flags & HA_NOSAME);
      }
      if (!is_excluded_key)
2093 2094 2095 2096 2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 2109 2110 2111 2112
      {
        do  /* For all equalities on all key parts */
        {
          /* Check if this is "t.keypart = expr(outer_tables) */
          if (!(keyuse->used_tables & sj_inner_tables) &&
              !(keyuse->optimize & KEY_OPTIMIZE_REF_OR_NULL))
          {
            bound_parts |= 1 << keyuse->keypart;
          }
          keyuse++;
        } while (keyuse->key == key && keyuse->table == table);

        if (bound_parts == PREV_BITS(uint, keyinfo->key_parts))
          return TRUE;
      }
      else
      {
        do
        {
          keyuse++;
2113
        } while (keyuse->key == key && keyuse->table == table);
2114
      }
2115
    } while (keyuse->table == table);
2116 2117 2118 2119
  }
  return FALSE;
}

2120

2121 2122 2123 2124 2125 2126 2127 2128 2129 2130 2131 2132 2133 2134 2135 2136 2137 2138 2139 2140 2141 2142 2143 2144 2145 2146 2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157 2158 2159 2160 2161 2162 2163 2164 2165 2166 2167 2168 2169 2170 2171 2172 2173 2174 2175 2176
/*
  Do semi-join optimization step after we've added a new tab to join prefix

  SYNOPSIS
    advance_sj_state()
      join                        The join we're optimizing
      remaining_tables            Tables not in the join prefix
      new_join_tab                Join tab we've just added to the join prefix
      idx                         Index of this join tab (i.e. number of tables
                                  in the prefix minus one)
      current_record_count INOUT  Estimate of #records in join prefix's output
      current_read_time    INOUT  Cost to execute the join prefix
      loose_scan_pos       IN     A POSITION with LooseScan plan to access 
                                  table new_join_tab
                                  (produced by the last best_access_path call)

  DESCRIPTION
    Update semi-join optimization state after we've added another tab (table 
    and access method) to the join prefix.
    
    The state is maintained in join->positions[#prefix_size]. Each of the
    available strategies has its own state variables.
    
    for each semi-join strategy
    {
      update strategy's state variables;

      if (join prefix has all the tables that are needed to consider
          using this strategy for the semi-join(s))
      {
        calculate cost of using the strategy
        if ((this is the first strategy to handle the semi-join nest(s)  ||
            the cost is less than other strategies))
        {
          // Pick this strategy
          pos->sj_strategy= ..
          ..
        }
      }

    Most of the new state is saved join->positions[idx] (and hence no undo
    is necessary). Several members of class JOIN are updated also, these
    changes can be rolled back with restore_prev_sj_state().

    See setup_semijoin_dups_elimination() for a description of what kinds of
    join prefixes each strategy can handle.
*/

void advance_sj_state(JOIN *join, table_map remaining_tables, 
                      const JOIN_TAB *new_join_tab, uint idx, 
                      double *current_record_count, double *current_read_time, 
                      POSITION *loose_scan_pos)
{
  TABLE_LIST *emb_sj_nest;
  POSITION *pos= join->positions + idx;
  remaining_tables &= ~new_join_tab->table->map;
2177
  bool disable_jbuf= join->thd->variables.join_cache_level == 0;
2178 2179 2180 2181 2182

  pos->prefix_cost.convert_from_cost(*current_read_time);
  pos->prefix_record_count= *current_record_count;
  pos->sj_strategy= SJ_OPT_NONE;
  
2183
  pos->prefix_dups_producing_tables= join->cur_dups_producing_tables;
2184 2185 2186 2187 2188 2189 2190 2191 2192 2193 2194

  /* We're performing optimization inside SJ-Materialization nest */
  if (join->emb_sjm_nest)
  {
    pos->invalidate_firstmatch_prefix();
    pos->first_loosescan_table= MAX_TABLES; 
    pos->dupsweedout_tables= 0;
    pos->sjm_scan_need_tables= 0;
    return;
  }

2195 2196 2197
  /* Initialize the state or copy it from prev. tables */
  if (idx == join->const_tables)
  {
2198
    pos->invalidate_firstmatch_prefix();
2199 2200 2201 2202 2203 2204 2205 2206 2207 2208 2209 2210 2211 2212 2213 2214 2215 2216 2217 2218 2219 2220 2221 2222 2223 2224 2225 2226 2227 2228 2229 2230 2231 2232
    pos->first_loosescan_table= MAX_TABLES; 
    pos->dupsweedout_tables= 0;
    pos->sjm_scan_need_tables= 0;
    LINT_INIT(pos->sjm_scan_last_inner);
  }
  else
  {
    // FirstMatch
    pos->first_firstmatch_table=
      (pos[-1].sj_strategy == SJ_OPT_FIRST_MATCH) ?
      MAX_TABLES : pos[-1].first_firstmatch_table;
    pos->first_firstmatch_rtbl= pos[-1].first_firstmatch_rtbl;
    pos->firstmatch_need_tables= pos[-1].firstmatch_need_tables;

    // LooseScan
    pos->first_loosescan_table=
      (pos[-1].sj_strategy == SJ_OPT_LOOSE_SCAN) ?
      MAX_TABLES : pos[-1].first_loosescan_table;
    pos->loosescan_need_tables= pos[-1].loosescan_need_tables;

    // SJ-Materialization Scan
    pos->sjm_scan_need_tables=
      (pos[-1].sj_strategy == SJ_OPT_MATERIALIZE_SCAN) ?
      0 : pos[-1].sjm_scan_need_tables;
    pos->sjm_scan_last_inner= pos[-1].sjm_scan_last_inner;

    // Duplicate Weedout
    pos->dupsweedout_tables=      pos[-1].dupsweedout_tables;
    pos->first_dupsweedout_table= pos[-1].first_dupsweedout_table;
  }
  
  table_map handled_by_fm_or_ls= 0;
  /* FirstMatch Strategy */
  if (new_join_tab->emb_sj_nest &&
2233 2234
      optimizer_flag(join->thd, OPTIMIZER_SWITCH_FIRSTMATCH) &&
      !join->outer_join)
2235 2236 2237 2238 2239
  {
    const table_map outer_corr_tables=
      new_join_tab->emb_sj_nest->nested_join->sj_corr_tables |
      new_join_tab->emb_sj_nest->nested_join->sj_depends_on;
    const table_map sj_inner_tables=
2240
      new_join_tab->emb_sj_nest->sj_inner_tables & ~join->const_table_map;
2241 2242 2243 2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254 2255 2256 2257 2258 2259 2260 2261 2262 2263

    /* 
      Enter condition:
       1. The next join tab belongs to semi-join nest
          (verified for the encompassing code block above).
       2. We're not in a duplicate producer range yet
       3. All outer tables that
           - the subquery is correlated with, or
           - referred to from the outer_expr 
          are in the join prefix
       4. All inner tables are still part of remaining_tables.
    */
    if (!join->cur_sj_inner_tables &&              // (2)
        !(remaining_tables & outer_corr_tables) && // (3)
        (sj_inner_tables ==                        // (4)
         ((remaining_tables | new_join_tab->table->map) & sj_inner_tables)))
    {
      /* Start tracking potential FirstMatch range */
      pos->first_firstmatch_table= idx;
      pos->firstmatch_need_tables= sj_inner_tables;
      pos->first_firstmatch_rtbl= remaining_tables;
    }

2264
    if (pos->in_firstmatch_prefix())
2265 2266 2267 2268 2269 2270 2271
    {
      if (outer_corr_tables & pos->first_firstmatch_rtbl)
      {
        /*
          Trying to add an sj-inner table whose sj-nest has an outer correlated 
          table that was not in the prefix. This means FirstMatch can't be used.
        */
2272
        pos->invalidate_firstmatch_prefix();
2273 2274 2275 2276 2277 2278 2279
      }
      else
      {
        /* Record that we need all of this semi-join's inner tables, too */
        pos->firstmatch_need_tables|= sj_inner_tables;
      }
    
2280 2281
      if (pos->in_firstmatch_prefix() && 
          !(pos->firstmatch_need_tables & remaining_tables))
2282 2283 2284 2285 2286 2287 2288
      {
        /*
          Got a complete FirstMatch range.
            Calculate correct costs and fanout
        */
        optimize_wo_join_buffering(join, pos->first_firstmatch_table, idx,
                                   remaining_tables, FALSE, idx,
2289 2290
                                   current_record_count, 
                                   current_read_time);
2291 2292 2293 2294 2295 2296 2297 2298 2299 2300 2301 2302 2303 2304 2305 2306 2307 2308 2309 2310 2311 2312 2313 2314 2315 2316 2317 2318 2319 2320 2321 2322 2323 2324 2325 2326 2327 2328
        /*
          We don't yet know what are the other strategies, so pick the
          FirstMatch.

          We ought to save the alternate POSITIONs produced by
          optimize_wo_join_buffering but the problem is that providing save
          space uses too much space. Instead, we will re-calculate the
          alternate POSITIONs after we've picked the best QEP.
        */
        pos->sj_strategy= SJ_OPT_FIRST_MATCH;
        handled_by_fm_or_ls=  pos->firstmatch_need_tables;
      }
    }
  }

  /* LooseScan Strategy */
  {
    POSITION *first=join->positions+pos->first_loosescan_table; 
    /* 
      LooseScan strategy can't handle interleaving between tables from the 
      semi-join that LooseScan is handling and any other tables.

      If we were considering LooseScan for the join prefix (1)
         and the table we're adding creates an interleaving (2)
      then 
         stop considering loose scan
    */
    if ((pos->first_loosescan_table != MAX_TABLES) &&   // (1)
        (first->table->emb_sj_nest->sj_inner_tables & remaining_tables) && //(2)
        new_join_tab->emb_sj_nest != first->table->emb_sj_nest) //(2)
    {
      pos->first_loosescan_table= MAX_TABLES;
    }

    /*
      If we got an option to use LooseScan for the current table, start
      considering using LooseScan strategy
    */
2329
    if (loose_scan_pos->read_time != DBL_MAX && !join->outer_join)
2330 2331 2332 2333 2334 2335 2336 2337 2338 2339 2340 2341 2342 2343 2344 2345 2346 2347 2348 2349 2350 2351 2352 2353 2354 2355 2356
    {
      pos->first_loosescan_table= idx;
      pos->loosescan_need_tables=
        new_join_tab->emb_sj_nest->sj_inner_tables | 
        new_join_tab->emb_sj_nest->nested_join->sj_depends_on |
        new_join_tab->emb_sj_nest->nested_join->sj_corr_tables;
    }
    
    if ((pos->first_loosescan_table != MAX_TABLES) && 
        !(remaining_tables & pos->loosescan_need_tables))
    {
      /* 
        Ok we have LooseScan plan and also have all LooseScan sj-nest's
        inner tables and outer correlated tables into the prefix.
      */

      first=join->positions + pos->first_loosescan_table; 
      uint n_tables= my_count_bits(first->table->emb_sj_nest->sj_inner_tables);
      /* Got a complete LooseScan range. Calculate its cost */
      /*
        The same problem as with FirstMatch - we need to save POSITIONs
        somewhere but reserving space for all cases would require too
        much space. We will re-calculate POSITION structures later on. 
      */
      optimize_wo_join_buffering(join, pos->first_loosescan_table, idx,
                                 remaining_tables, 
                                 TRUE,  //first_alt
2357
                                 disable_jbuf ? join->table_count :
2358
                                   pos->first_loosescan_table + n_tables,
2359 2360
                                 current_record_count,
                                 current_read_time);
2361 2362 2363 2364 2365 2366 2367 2368 2369 2370 2371 2372 2373 2374 2375 2376 2377 2378 2379 2380 2381 2382 2383 2384 2385 2386 2387 2388 2389 2390 2391 2392 2393 2394 2395 2396 2397 2398 2399 2400 2401 2402 2403 2404 2405 2406 2407 2408 2409 2410 2411 2412 2413 2414 2415 2416 2417 2418 2419 2420 2421 2422 2423 2424 2425 2426 2427 2428 2429 2430 2431 2432 2433 2434 2435 2436 2437 2438 2439 2440 2441 2442 2443 2444 2445 2446 2447 2448 2449 2450 2451 2452 2453 2454 2455 2456 2457 2458 2459 2460 2461 2462 2463 2464 2465 2466 2467 2468 2469 2470 2471 2472 2473 2474 2475 2476 2477 2478 2479 2480 2481 2482 2483 2484 2485 2486 2487 2488 2489 2490 2491 2492 2493 2494 2495 2496
      /*
        We don't yet have any other strategies that could handle this
        semi-join nest (the other options are Duplicate Elimination or
        Materialization, which need at least the same set of tables in 
        the join prefix to be considered) so unconditionally pick the 
        LooseScan.
      */
      pos->sj_strategy= SJ_OPT_LOOSE_SCAN;
      handled_by_fm_or_ls= first->table->emb_sj_nest->sj_inner_tables;
    }
  }

  /* 
    Update join->cur_sj_inner_tables (Used by FirstMatch in this function and
    LooseScan detector in best_access_path)
  */
  if ((emb_sj_nest= new_join_tab->emb_sj_nest))
  {
    join->cur_sj_inner_tables |= emb_sj_nest->sj_inner_tables;
    join->cur_dups_producing_tables |= emb_sj_nest->sj_inner_tables;

    /* Remove the sj_nest if all of its SJ-inner tables are in cur_table_map */
    if (!(remaining_tables &
          emb_sj_nest->sj_inner_tables & ~new_join_tab->table->map))
      join->cur_sj_inner_tables &= ~emb_sj_nest->sj_inner_tables;
  }
  join->cur_dups_producing_tables &= ~handled_by_fm_or_ls;

  /* 4. SJ-Materialization and SJ-Materialization-scan strategy handler */
  bool sjm_scan;
  SJ_MATERIALIZATION_INFO *mat_info;
  if ((mat_info= at_sjmat_pos(join, remaining_tables,
                              new_join_tab, idx, &sjm_scan)))
  {
    if (sjm_scan)
    {
      /*
        We can't yet evaluate this option yet. This is because we can't
        accout for fanout of sj-inner tables yet:

          ntX  SJM-SCAN(it1 ... itN) | ot1 ... otN  |
                                     ^(1)           ^(2)

        we're now at position (1). SJM temptable in general has multiple
        records, so at point (1) we'll get the fanout from sj-inner tables (ie
        there will be multiple record combinations).

        The final join result will not contain any semi-join produced
        fanout, i.e. tables within SJM-SCAN(...) will not contribute to
        the cardinality of the join output.  Extra fanout produced by 
        SJM-SCAN(...) will be 'absorbed' into fanout produced by ot1 ...  otN.

        The simple way to model this is to remove SJM-SCAN(...) fanout once
        we reach the point #2.
      */
      pos->sjm_scan_need_tables=
        new_join_tab->emb_sj_nest->sj_inner_tables | 
        new_join_tab->emb_sj_nest->nested_join->sj_depends_on |
        new_join_tab->emb_sj_nest->nested_join->sj_corr_tables;
      pos->sjm_scan_last_inner= idx;
    }
    else
    {
      /* This is SJ-Materialization with lookups */
      COST_VECT prefix_cost; 
      signed int first_tab= (int)idx - mat_info->tables;
      double prefix_rec_count;
      if (first_tab < (int)join->const_tables)
      {
        prefix_cost.zero();
        prefix_rec_count= 1.0;
      }
      else
      {
        prefix_cost= join->positions[first_tab].prefix_cost;
        prefix_rec_count= join->positions[first_tab].prefix_record_count;
      }

      double mat_read_time= prefix_cost.total_cost();
      mat_read_time += mat_info->materialization_cost.total_cost() +
                       prefix_rec_count * mat_info->lookup_cost.total_cost();

      if (mat_read_time < *current_read_time || join->cur_dups_producing_tables)
      {
        /*
          NOTE: When we pick to use SJM[-Scan] we don't memcpy its POSITION
          elements to join->positions as that makes it hard to return things
          back when making one step back in join optimization. That's done 
          after the QEP has been chosen.
        */
        pos->sj_strategy= SJ_OPT_MATERIALIZE;
        *current_read_time=    mat_read_time;
        *current_record_count= prefix_rec_count;
        join->cur_dups_producing_tables&=
          ~new_join_tab->emb_sj_nest->sj_inner_tables;
      }
    }
  }
  
  /* 4.A SJM-Scan second phase check */
  if (pos->sjm_scan_need_tables && /* Have SJM-Scan prefix */
      !(pos->sjm_scan_need_tables & remaining_tables))
  {
    TABLE_LIST *mat_nest= 
      join->positions[pos->sjm_scan_last_inner].table->emb_sj_nest;
    SJ_MATERIALIZATION_INFO *mat_info= mat_nest->sj_mat_info;

    double prefix_cost;
    double prefix_rec_count;
    int first_tab= pos->sjm_scan_last_inner + 1 - mat_info->tables;
    /* Get the prefix cost */
    if (first_tab == (int)join->const_tables)
    {
      prefix_rec_count= 1.0;
      prefix_cost= 0.0;
    }
    else
    {
      prefix_cost= join->positions[first_tab - 1].prefix_cost.total_cost();
      prefix_rec_count= join->positions[first_tab - 1].prefix_record_count;
    }

    /* Add materialization cost */
    prefix_cost += mat_info->materialization_cost.total_cost() +
                   prefix_rec_count * mat_info->scan_cost.total_cost();
    prefix_rec_count *= mat_info->rows;
    
    uint i;
    table_map rem_tables= remaining_tables;
    for (i= idx; i != (first_tab + mat_info->tables - 1); i--)
      rem_tables |= join->positions[i].table->table->map;

    POSITION curpos, dummy;
    /* Need to re-run best-access-path as we prefix_rec_count has changed */
    for (i= first_tab + mat_info->tables; i <= idx; i++)
    {
2497 2498
      best_access_path(join, join->positions[i].table, rem_tables, i,
                       disable_jbuf, prefix_rec_count, &curpos, &dummy);
2499 2500 2501 2502 2503 2504 2505 2506 2507 2508 2509 2510 2511 2512 2513 2514 2515 2516 2517 2518 2519 2520 2521 2522 2523 2524 2525 2526 2527 2528 2529 2530 2531 2532 2533 2534 2535 2536
      prefix_rec_count *= curpos.records_read;
      prefix_cost += curpos.read_time;
    }

    /*
      Use the strategy if 
       * it is cheaper then what we've had, or
       * we haven't picked any other semi-join strategy yet
      In the second case, we pick this strategy unconditionally because
      comparing cost without semi-join duplicate removal with cost with
      duplicate removal is not an apples-to-apples comparison.
    */
    if (prefix_cost < *current_read_time || join->cur_dups_producing_tables)
    {
      pos->sj_strategy= SJ_OPT_MATERIALIZE_SCAN;
      *current_read_time=    prefix_cost;
      *current_record_count= prefix_rec_count;
      join->cur_dups_producing_tables&= ~mat_nest->sj_inner_tables;

    }
  }

  /* 5. Duplicate Weedout strategy handler */
  {
    /* 
       Duplicate weedout can be applied after all ON-correlated and 
       correlated 
    */
    TABLE_LIST *nest;
    if ((nest= new_join_tab->emb_sj_nest))
    {
      if (!pos->dupsweedout_tables)
        pos->first_dupsweedout_table= idx;

      pos->dupsweedout_tables |= nest->sj_inner_tables |
                                 nest->nested_join->sj_depends_on |
                                 nest->nested_join->sj_corr_tables;
    }
2537 2538 2539 2540 2541 2542 2543 2544 2545
    
    if (pos->dupsweedout_tables)
    {
      /* we're in the process of constructing a DuplicateWeedout range */
      TABLE_LIST *emb= new_join_tab->table->pos_in_table_list->embedding;
      /* and we've entered an inner side of an outer join*/
      if (emb && emb->on_expr)
        pos->dupsweedout_tables |= emb->nested_join->used_tables;
    }
2546 2547 2548 2549 2550 2551 2552 2553 2554 2555 2556 2557 2558 2559 2560 2561 2562 2563 2564 2565 2566 2567 2568 2569 2570 2571 2572 2573 2574 2575 2576 2577 2578 2579 2580 2581 2582 2583 2584 2585 2586 2587 2588 2589 2590 2591 2592 2593 2594 2595 2596 2597 2598 2599 2600 2601 2602 2603 2604 2605 2606 2607

    if (pos->dupsweedout_tables && 
        !(remaining_tables &
          ~new_join_tab->table->map & pos->dupsweedout_tables))
    {
      /*
        Ok, reached a state where we could put a dups weedout point.
        Walk back and calculate
          - the join cost (this is needed as the accumulated cost may assume 
            some other duplicate elimination method)
          - extra fanout that will be removed by duplicate elimination
          - duplicate elimination cost
        There are two cases:
          1. We have other strategy/ies to remove all of the duplicates.
          2. We don't.
        
        We need to calculate the cost in case #2 also because we need to make
        choice between this join order and others.
      */
      uint first_tab= pos->first_dupsweedout_table;
      double dups_cost;
      double prefix_rec_count;
      double sj_inner_fanout= 1.0;
      double sj_outer_fanout= 1.0;
      uint temptable_rec_size;
      if (first_tab == join->const_tables)
      {
        prefix_rec_count= 1.0;
        temptable_rec_size= 0;
        dups_cost= 0.0;
      }
      else
      {
        dups_cost= join->positions[first_tab - 1].prefix_cost.total_cost();
        prefix_rec_count= join->positions[first_tab - 1].prefix_record_count;
        temptable_rec_size= 8; /* This is not true but we'll make it so */
      }
      
      table_map dups_removed_fanout= 0;
      for (uint j= pos->first_dupsweedout_table; j <= idx; j++)
      {
        POSITION *p= join->positions + j;
        dups_cost += p->read_time;
        if (p->table->emb_sj_nest)
        {
          sj_inner_fanout *= p->records_read;
          dups_removed_fanout |= p->table->table->map;
        }
        else
        {
          sj_outer_fanout *= p->records_read;
          temptable_rec_size += p->table->table->file->ref_length;
        }
      }

      /*
        Add the cost of temptable use. The table will have sj_outer_fanout
        records, and we will make 
        - sj_outer_fanout table writes
        - sj_inner_fanout*sj_outer_fanout  lookups.

      */
unknown's avatar
unknown committed
2608 2609 2610 2611 2612 2613
      double one_lookup_cost= get_tmp_table_lookup_cost(join->thd,
                                                        sj_outer_fanout,
                                                        temptable_rec_size);
      double one_write_cost= get_tmp_table_write_cost(join->thd,
                                                      sj_outer_fanout,
                                                      temptable_rec_size);
2614 2615

      double write_cost= join->positions[first_tab].prefix_record_count* 
unknown's avatar
unknown committed
2616
                         sj_outer_fanout * one_write_cost;
2617 2618 2619 2620 2621 2622 2623 2624 2625 2626 2627 2628 2629 2630 2631 2632 2633
      double full_lookup_cost= join->positions[first_tab].prefix_record_count* 
                               sj_outer_fanout* sj_inner_fanout * 
                               one_lookup_cost;
      dups_cost += write_cost + full_lookup_cost;
      
      /*
        Use the strategy if 
         * it is cheaper then what we've had, or
         * we haven't picked any other semi-join strategy yet
        The second part is necessary because this strategy is the last one
        to consider (it needs "the most" tables in the prefix) and we can't
        leave duplicate-producing tables not handled by any strategy.
      */
      if (dups_cost < *current_read_time || join->cur_dups_producing_tables)
      {
        pos->sj_strategy= SJ_OPT_DUPS_WEEDOUT;
        *current_read_time= dups_cost;
2634
        *current_record_count= prefix_rec_count * sj_outer_fanout;
2635 2636 2637 2638 2639 2640 2641 2642 2643 2644 2645 2646 2647 2648 2649 2650 2651 2652 2653 2654 2655 2656 2657 2658 2659
        join->cur_dups_producing_tables &= ~dups_removed_fanout;
      }
    }
  }
}


/*
  Remove the last join tab from from join->cur_sj_inner_tables bitmap
  we assume remaining_tables doesnt contain @tab.
*/

void restore_prev_sj_state(const table_map remaining_tables, 
                                  const JOIN_TAB *tab, uint idx)
{
  TABLE_LIST *emb_sj_nest;
  if ((emb_sj_nest= tab->emb_sj_nest))
  {
    /* If we're removing the last SJ-inner table, remove the sj-nest */
    if ((remaining_tables & emb_sj_nest->sj_inner_tables) == 
        (emb_sj_nest->sj_inner_tables & ~tab->table->map))
    {
      tab->join->cur_sj_inner_tables &= ~emb_sj_nest->sj_inner_tables;
    }
  }
2660 2661
  POSITION *pos= tab->join->positions + idx;
  tab->join->cur_dups_producing_tables= pos->prefix_dups_producing_tables;
2662 2663 2664 2665 2666 2667 2668 2669 2670 2671 2672 2673 2674 2675 2676 2677 2678 2679 2680 2681 2682 2683 2684 2685 2686 2687 2688 2689 2690 2691 2692 2693 2694 2695 2696 2697 2698 2699 2700
}


/*
  Given a semi-join nest, find out which of the IN-equalities are bound

  SYNOPSIS
    get_bound_sj_equalities()
      sj_nest           Semi-join nest
      remaining_tables  Tables that are not yet bound

  DESCRIPTION
    Given a semi-join nest, find out which of the IN-equalities have their
    left part expression bound (i.e. the said expression doesn't refer to
    any of remaining_tables and can be evaluated).

  RETURN
    Bitmap of bound IN-equalities.
*/

ulonglong get_bound_sj_equalities(TABLE_LIST *sj_nest, 
                                  table_map remaining_tables)
{
  List_iterator<Item> li(sj_nest->nested_join->sj_outer_expr_list);
  Item *item;
  uint i= 0;
  ulonglong res= 0;
  while ((item= li++))
  {
    /*
      Q: should this take into account equality propagation and how?
      A: If e->outer_side is an Item_field, walk over the equality
         class and see if there is an element that is bound?
      (this is an optional feature)
    */
    if (!(item->used_tables() & remaining_tables))
    {
      res |= 1ULL << i;
    }
2701
    i++;
2702 2703 2704 2705 2706 2707 2708 2709 2710 2711 2712 2713 2714 2715 2716 2717 2718 2719 2720 2721 2722 2723 2724 2725 2726 2727 2728 2729 2730 2731 2732 2733 2734 2735 2736 2737 2738 2739 2740 2741 2742 2743 2744 2745 2746 2747 2748 2749 2750 2751 2752 2753 2754 2755 2756 2757 2758 2759 2760 2761 2762 2763 2764 2765 2766 2767 2768 2769 2770 2771 2772 2773 2774 2775 2776 2777 2778 2779 2780 2781 2782 2783 2784 2785 2786 2787 2788 2789 2790 2791 2792 2793 2794 2795 2796 2797 2798 2799 2800 2801 2802 2803 2804
  }
  return res;
}


/*
  Check if the last tables of the partial join order allow to use
  sj-materialization strategy for them

  SYNOPSIS
    at_sjmat_pos()
      join              
      remaining_tables
      tab                the last table's join tab
      idx                last table's index
      loose_scan    OUT  TRUE <=> use LooseScan

  RETURN
    TRUE   Yes, can apply sj-materialization
    FALSE  No, some of the requirements are not met
*/

static SJ_MATERIALIZATION_INFO *
at_sjmat_pos(const JOIN *join, table_map remaining_tables, const JOIN_TAB *tab,
             uint idx, bool *loose_scan)
{
  /*
   Check if 
    1. We're in a semi-join nest that can be run with SJ-materialization
    2. All the tables correlated through the IN subquery are in the prefix
  */
  TABLE_LIST *emb_sj_nest= tab->emb_sj_nest;
  table_map suffix= remaining_tables & ~tab->table->map;
  if (emb_sj_nest && emb_sj_nest->sj_mat_info &&
      !(suffix & emb_sj_nest->sj_inner_tables))
  {
    /* 
      Walk back and check if all immediately preceding tables are from
      this semi-join.
    */
    uint n_tables= my_count_bits(tab->emb_sj_nest->sj_inner_tables);
    for (uint i= 1; i < n_tables ; i++)
    {
      if (join->positions[idx - i].table->emb_sj_nest != tab->emb_sj_nest)
        return NULL;
    }
    *loose_scan= test(remaining_tables & ~tab->table->map &
                             (emb_sj_nest->sj_inner_tables |
                              emb_sj_nest->nested_join->sj_depends_on));
    if (*loose_scan && !emb_sj_nest->sj_subq_pred->sjm_scan_allowed)
      return NULL;
    else
      return emb_sj_nest->sj_mat_info;
  }
  return NULL;
}



/*
  Fix semi-join strategies for the picked join order

  SYNOPSIS
    fix_semijoin_strategies_for_picked_join_order()
      join  The join with the picked join order

  DESCRIPTION
    Fix semi-join strategies for the picked join order. This is a step that
    needs to be done right after we have fixed the join order. What we do
    here is switch join's semi-join strategy description from backward-based
    to forwards based.
    
    When join optimization is in progress, we re-consider semi-join
    strategies after we've added another table. Here's an illustration.
    Suppose the join optimization is underway:

    1) ot1  it1  it2 
                 sjX  -- looking at (ot1, it1, it2) join prefix, we decide
                         to use semi-join strategy sjX.

    2) ot1  it1  it2  ot2 
                 sjX  sjY -- Having added table ot2, we now may consider
                             another semi-join strategy and decide to use a 
                             different strategy sjY. Note that the record
                             of sjX has remained under it2. That is
                             necessary because we need to be able to get
                             back to (ot1, it1, it2) join prefix.
      what makes things even worse is that there are cases where the choice
      of sjY changes the way we should access it2. 

    3) [ot1  it1  it2  ot2  ot3]
                  sjX  sjY  -- This means that after join optimization is
                               finished, semi-join info should be read
                               right-to-left (while nearly all plan refinement
                               functions, EXPLAIN, etc proceed from left to 
                               right)

    This function does the needed reversal, making it possible to read the
    join and semi-join order from left to right.
*/    

void fix_semijoin_strategies_for_picked_join_order(JOIN *join)
{
2805
  uint table_count=join->table_count;
2806 2807 2808 2809 2810 2811 2812 2813 2814 2815 2816 2817 2818 2819 2820 2821 2822 2823 2824 2825 2826 2827 2828 2829 2830 2831 2832 2833 2834 2835 2836 2837 2838 2839 2840 2841 2842 2843 2844 2845 2846 2847 2848 2849 2850 2851 2852 2853 2854 2855 2856 2857 2858 2859 2860 2861 2862 2863 2864 2865 2866
  uint tablenr;
  table_map remaining_tables= 0;
  table_map handled_tabs= 0;
  for (tablenr= table_count - 1 ; tablenr != join->const_tables - 1; tablenr--)
  {
    POSITION *pos= join->best_positions + tablenr;
    JOIN_TAB *s= pos->table;
    uint first;
    LINT_INIT(first); // Set by every branch except SJ_OPT_NONE which doesn't use it

    if ((handled_tabs & s->table->map) || pos->sj_strategy == SJ_OPT_NONE)
    {
      remaining_tables |= s->table->map;
      continue;
    }
    
    if (pos->sj_strategy == SJ_OPT_MATERIALIZE)
    {
      SJ_MATERIALIZATION_INFO *sjm= s->emb_sj_nest->sj_mat_info;
      sjm->is_used= TRUE;
      sjm->is_sj_scan= FALSE;
      memcpy(pos - sjm->tables + 1, sjm->positions, 
             sizeof(POSITION) * sjm->tables);
      first= tablenr - sjm->tables + 1;
      join->best_positions[first].n_sj_tables= sjm->tables;
      join->best_positions[first].sj_strategy= SJ_OPT_MATERIALIZE;
    }
    else if (pos->sj_strategy == SJ_OPT_MATERIALIZE_SCAN)
    {
      POSITION *first_inner= join->best_positions + pos->sjm_scan_last_inner;
      SJ_MATERIALIZATION_INFO *sjm= first_inner->table->emb_sj_nest->sj_mat_info;
      sjm->is_used= TRUE;
      sjm->is_sj_scan= TRUE;
      first= pos->sjm_scan_last_inner - sjm->tables + 1;
      memcpy(join->best_positions + first, 
             sjm->positions, sizeof(POSITION) * sjm->tables);
      join->best_positions[first].sj_strategy= SJ_OPT_MATERIALIZE_SCAN;
      join->best_positions[first].n_sj_tables= sjm->tables;
      /* 
        Do what advance_sj_state did: re-run best_access_path for every table
        in the [last_inner_table + 1; pos..) range
      */
      double prefix_rec_count;
      /* Get the prefix record count */
      if (first == join->const_tables)
        prefix_rec_count= 1.0;
      else
        prefix_rec_count= join->best_positions[first-1].prefix_record_count;
      
      /* Add materialization record count*/
      prefix_rec_count *= sjm->rows;
      
      uint i;
      table_map rem_tables= remaining_tables;
      for (i= tablenr; i != (first + sjm->tables - 1); i--)
        rem_tables |= join->best_positions[i].table->table->map;

      POSITION dummy;
      join->cur_sj_inner_tables= 0;
      for (i= first + sjm->tables; i <= tablenr; i++)
      {
2867 2868
        best_access_path(join, join->best_positions[i].table, rem_tables, i, 
                         FALSE, prefix_rec_count,
2869
                         join->best_positions + i, &dummy);
2870 2871 2872 2873 2874 2875 2876 2877 2878 2879 2880 2881 2882 2883 2884 2885 2886 2887 2888 2889 2890 2891 2892 2893 2894 2895 2896 2897 2898 2899 2900 2901 2902 2903 2904 2905 2906 2907 2908 2909 2910 2911 2912 2913 2914 2915 2916 2917 2918 2919 2920 2921 2922 2923 2924 2925 2926 2927 2928 2929 2930 2931 2932 2933 2934 2935 2936 2937 2938 2939 2940 2941 2942 2943 2944 2945 2946 2947 2948 2949 2950 2951 2952 2953 2954 2955 2956 2957 2958 2959 2960 2961 2962 2963 2964
        prefix_rec_count *= join->best_positions[i].records_read;
        rem_tables &= ~join->best_positions[i].table->table->map;
      }
    }
 
    if (pos->sj_strategy == SJ_OPT_FIRST_MATCH)
    {
      first= pos->first_firstmatch_table;
      join->best_positions[first].sj_strategy= SJ_OPT_FIRST_MATCH;
      join->best_positions[first].n_sj_tables= tablenr - first + 1;
      POSITION dummy; // For loose scan paths
      double record_count= (first== join->const_tables)? 1.0: 
                           join->best_positions[tablenr - 1].prefix_record_count;
      
      table_map rem_tables= remaining_tables;
      uint idx;
      for (idx= first; idx <= tablenr; idx++)
      {
        rem_tables |= join->best_positions[idx].table->table->map;
      }
      /*
        Re-run best_access_path to produce best access methods that do not use
        join buffering
      */ 
      join->cur_sj_inner_tables= 0;
      for (idx= first; idx <= tablenr; idx++)
      {
        if (join->best_positions[idx].use_join_buffer)
        {
           best_access_path(join, join->best_positions[idx].table, 
                            rem_tables, idx, TRUE /* no jbuf */,
                            record_count, join->best_positions + idx, &dummy);
        }
        record_count *= join->best_positions[idx].records_read;
        rem_tables &= ~join->best_positions[idx].table->table->map;
      }
    }

    if (pos->sj_strategy == SJ_OPT_LOOSE_SCAN) 
    {
      first= pos->first_loosescan_table;
      POSITION *first_pos= join->best_positions + first;
      POSITION loose_scan_pos; // For loose scan paths
      double record_count= (first== join->const_tables)? 1.0: 
                           join->best_positions[tablenr - 1].prefix_record_count;
      
      table_map rem_tables= remaining_tables;
      uint idx;
      for (idx= first; idx <= tablenr; idx++)
        rem_tables |= join->best_positions[idx].table->table->map;
      /*
        Re-run best_access_path to produce best access methods that do not use
        join buffering
      */ 
      join->cur_sj_inner_tables= 0;
      for (idx= first; idx <= tablenr; idx++)
      {
        if (join->best_positions[idx].use_join_buffer || (idx == first))
        {
           best_access_path(join, join->best_positions[idx].table,
                            rem_tables, idx, TRUE /* no jbuf */,
                            record_count, join->best_positions + idx,
                            &loose_scan_pos);
           if (idx==first)
             join->best_positions[idx]= loose_scan_pos;
        }
        rem_tables &= ~join->best_positions[idx].table->table->map;
        record_count *= join->best_positions[idx].records_read;
      }
      first_pos->sj_strategy= SJ_OPT_LOOSE_SCAN;
      first_pos->n_sj_tables= my_count_bits(first_pos->table->emb_sj_nest->sj_inner_tables);
    }

    if (pos->sj_strategy == SJ_OPT_DUPS_WEEDOUT)
    {
      /* 
        Duplicate Weedout starting at pos->first_dupsweedout_table, ending at
        this table.
      */
      first= pos->first_dupsweedout_table;
      join->best_positions[first].sj_strategy= SJ_OPT_DUPS_WEEDOUT;
      join->best_positions[first].n_sj_tables= tablenr - first + 1;
    }
    
    uint i_end= first + join->best_positions[first].n_sj_tables;
    for (uint i= first; i < i_end; i++)
    {
      if (i != first)
        join->best_positions[i].sj_strategy= SJ_OPT_NONE;
      handled_tabs |= join->best_positions[i].table->table->map;
    }

    if (tablenr != first)
      pos->sj_strategy= SJ_OPT_NONE;
    remaining_tables |= s->table->map;
2965 2966
    //s->sj_strategy= pos->sj_strategy;
    join->join_tab[first].sj_strategy= join->best_positions[first].sj_strategy;
Sergey Petrunya's avatar
Sergey Petrunya committed
2967
    join->join_tab[first].n_sj_tables= join->best_positions[first].n_sj_tables;
2968 2969 2970
  }
}

2971

2972 2973 2974 2975 2976 2977 2978 2979 2980 2981 2982 2983 2984 2985 2986 2987 2988 2989 2990 2991 2992
/*
  Setup semi-join materialization strategy for one semi-join nest
  
  SYNOPSIS

  setup_sj_materialization()
    tab  The first tab in the semi-join

  DESCRIPTION
    Setup execution structures for one semi-join materialization nest:
    - Create the materialization temporary table
    - If we're going to do index lookups
        create TABLE_REF structure to make the lookus
    - else (if we're going to do a full scan of the temptable)
        create Copy_field structures to do copying.

  RETURN
    FALSE  Ok
    TRUE   Error
*/

2993
bool setup_sj_materialization_part1(JOIN_TAB *sjm_tab)
2994 2995
{
  DBUG_ENTER("setup_sj_materialization");
2996
  JOIN_TAB *tab= sjm_tab->bush_children->start;
2997
  TABLE_LIST *emb_sj_nest= tab->table->pos_in_table_list->embedding;
2998 2999 3000 3001 3002
  
  /* Walk out of outer join nests until we reach the semi-join nest we're in */
  while (!emb_sj_nest->sj_mat_info)
    emb_sj_nest= emb_sj_nest->embedding;

3003 3004 3005
  SJ_MATERIALIZATION_INFO *sjm= emb_sj_nest->sj_mat_info;
  THD *thd= tab->join->thd;
  /* First the calls come to the materialization function */
3006
  //List<Item> &item_list= emb_sj_nest->sj_subq_pred->unit->first_select()->item_list;
3007 3008
  
  DBUG_ASSERT(sjm->is_used);
3009 3010 3011 3012
  /* 
    Set up the table to write to, do as select_union::create_result_table does
  */
  sjm->sjm_table_param.init();
3013
  sjm->sjm_table_param.bit_fields_as_long= TRUE;
3014 3015 3016 3017 3018 3019 3020 3021 3022
  //List_iterator<Item> it(item_list);
  SELECT_LEX *subq_select= emb_sj_nest->sj_subq_pred->unit->first_select();
  Item **p_item= subq_select->ref_pointer_array;
  Item **p_end= p_item + subq_select->item_list.elements;
  //while((right_expr= it++))
  for(;p_item != p_end; p_item++)
    sjm->sjm_table_cols.push_back(*p_item);

  sjm->sjm_table_param.field_count= subq_select->item_list.elements;
3023 3024 3025 3026 3027 3028 3029 3030 3031 3032 3033

  if (!(sjm->table= create_tmp_table(thd, &sjm->sjm_table_param, 
                                     sjm->sjm_table_cols, (ORDER*) 0, 
                                     TRUE /* distinct */, 
                                     1, /*save_sum_fields*/
                                     thd->options | TMP_TABLE_ALL_COLUMNS, 
                                     HA_POS_ERROR /*rows_limit */, 
                                     (char*)"sj-materialize")))
    DBUG_RETURN(TRUE); /* purecov: inspected */
  sjm->table->file->extra(HA_EXTRA_WRITE_CACHE);
  sjm->table->file->extra(HA_EXTRA_IGNORE_DUP_KEY);
Sergey Petrunya's avatar
Sergey Petrunya committed
3034

3035 3036 3037 3038
  tab->join->sj_tmp_tables.push_back(sjm->table);
  tab->join->sjm_info_list.push_back(sjm);
  
  sjm->materialized= FALSE;
3039
  sjm_tab->table= sjm->table;
Sergey Petrunya's avatar
Sergey Petrunya committed
3040
  sjm->table->pos_in_table_list= emb_sj_nest;
3041 3042 3043 3044 3045 3046 3047 3048 3049 3050
 
  DBUG_RETURN(FALSE);
}


bool setup_sj_materialization_part2(JOIN_TAB *sjm_tab)
{
  DBUG_ENTER("setup_sj_materialization_part2");
  JOIN_TAB *tab= sjm_tab->bush_children->start;
  TABLE_LIST *emb_sj_nest= tab->table->pos_in_table_list->embedding;
3051 3052 3053
  /* Walk out of outer join nests until we reach the semi-join nest we're in */
  while (!emb_sj_nest->sj_mat_info)
    emb_sj_nest= emb_sj_nest->embedding;
3054 3055 3056
  SJ_MATERIALIZATION_INFO *sjm= emb_sj_nest->sj_mat_info;
  THD *thd= tab->join->thd;
  uint i;
3057 3058
  //List<Item> &item_list= emb_sj_nest->sj_subq_pred->unit->first_select()->item_list;
  //List_iterator<Item> it(item_list);
3059

3060 3061 3062 3063 3064 3065 3066 3067 3068 3069 3070 3071
  if (!sjm->is_sj_scan)
  {
    KEY           *tmp_key; /* The only index on the temporary table. */
    uint          tmp_key_parts; /* Number of keyparts in tmp_key. */
    tmp_key= sjm->table->key_info;
    tmp_key_parts= tmp_key->key_parts;
    
    /*
      Create/initialize everything we will need to index lookups into the
      temptable.
    */
    TABLE_REF *tab_ref;
3072
    tab_ref= &sjm_tab->ref;
3073 3074 3075 3076 3077 3078 3079 3080 3081 3082 3083 3084 3085 3086 3087 3088 3089 3090 3091 3092 3093 3094 3095 3096 3097 3098 3099 3100 3101 3102 3103 3104
    tab_ref->key= 0; /* The only temp table index. */
    tab_ref->key_length= tmp_key->key_length;
    if (!(tab_ref->key_buff=
          (uchar*) thd->calloc(ALIGN_SIZE(tmp_key->key_length) * 2)) ||
        !(tab_ref->key_copy=
          (store_key**) thd->alloc((sizeof(store_key*) *
                                    (tmp_key_parts + 1)))) ||
        !(tab_ref->items=
          (Item**) thd->alloc(sizeof(Item*) * tmp_key_parts)))
      DBUG_RETURN(TRUE); /* purecov: inspected */

    tab_ref->key_buff2=tab_ref->key_buff+ALIGN_SIZE(tmp_key->key_length);
    tab_ref->key_err=1;
    tab_ref->null_rejecting= 1;
    tab_ref->disable_cache= FALSE;

    KEY_PART_INFO *cur_key_part= tmp_key->key_part;
    store_key **ref_key= tab_ref->key_copy;
    uchar *cur_ref_buff= tab_ref->key_buff;
    
    for (i= 0; i < tmp_key_parts; i++, cur_key_part++, ref_key++)
    {
      tab_ref->items[i]= emb_sj_nest->sj_subq_pred->left_expr->element_index(i);
      int null_count= test(cur_key_part->field->real_maybe_null());
      *ref_key= new store_key_item(thd, cur_key_part->field,
                                   /* TODO:
                                      the NULL byte is taken into account in
                                      cur_key_part->store_length, so instead of
                                      cur_ref_buff + test(maybe_null), we could
                                      use that information instead.
                                   */
                                   cur_ref_buff + null_count,
3105
                                   null_count ? cur_ref_buff : 0,
unknown's avatar
unknown committed
3106 3107
                                   cur_key_part->length, tab_ref->items[i],
                                   FALSE);
3108 3109 3110
      cur_ref_buff+= cur_key_part->store_length;
    }
    *ref_key= NULL; /* End marker. */
Sergey Petrunya's avatar
Sergey Petrunya committed
3111 3112 3113 3114 3115 3116 3117 3118 3119 3120
      
    /*
      We don't ever have guarded conditions for SJM tables, but code at SQL
      layer depends on cond_guards array being alloced.
    */
    if (!(tab_ref->cond_guards= (bool**) thd->calloc(sizeof(uint*)*tmp_key_parts)))
    {
      DBUG_RETURN(TRUE);
    }

3121 3122 3123 3124 3125 3126 3127 3128 3129 3130 3131 3132 3133 3134 3135 3136 3137 3138 3139
    tab_ref->key_err= 1;
    tab_ref->key_parts= tmp_key_parts;
    sjm->tab_ref= tab_ref;

    /*
      Remove the injected semi-join IN-equalities from join_tab conds. This
      needs to be done because the IN-equalities refer to columns of
      sj-inner tables which are not available after the materialization
      has been finished.
    */
    for (i= 0; i < sjm->tables; i++)
    {
      remove_sj_conds(&tab[i].select_cond);
      if (tab[i].select)
        remove_sj_conds(&tab[i].select->cond);
    }
    if (!(sjm->in_equality= create_subq_in_equalities(thd, sjm,
                                                      emb_sj_nest->sj_subq_pred)))
      DBUG_RETURN(TRUE); /* purecov: inspected */
3140
    sjm_tab->type= JT_EQ_REF;
Sergey Petrunya's avatar
Sergey Petrunya committed
3141
    sjm_tab->select_cond= sjm->in_equality;
3142 3143 3144 3145 3146 3147 3148 3149 3150 3151 3152 3153 3154 3155 3156 3157 3158 3159 3160 3161 3162 3163 3164 3165 3166 3167 3168 3169 3170 3171 3172
  }
  else
  {
    /*
      We'll be doing full scan of the temptable.  
      Setup copying of temptable columns back to the record buffers
      for their source tables. We need this because IN-equalities
      refer to the original tables.

      EXAMPLE

      Consider the query:
        SELECT * FROM ot WHERE ot.col1 IN (SELECT it.col2 FROM it)
      
      Suppose it's executed with SJ-Materialization-scan. We choose to do scan
      if we can't do the lookup, i.e. the join order is (it, ot). The plan
      would look as follows:

        table    access method      condition
         it      materialize+scan    -
         ot      (whatever)          ot1.col1=it.col2 (C2)

      The condition C2 refers to current row of table it. The problem is
      that by the time we evaluate C2, we would have finished with scanning
      it itself and will be scanning the temptable. 

      At the moment, our solution is to copy back: when we get the next
      temptable record, we copy its columns to their corresponding columns
      in the record buffers for the source tables. 
    */
    sjm->copy_field= new Copy_field[sjm->sjm_table_cols.elements];
3173
    //it.rewind();
3174
    Item **p_item= emb_sj_nest->sj_subq_pred->unit->first_select()->ref_pointer_array;
3175 3176 3177 3178
    for (uint i=0; i < sjm->sjm_table_cols.elements; i++)
    {
      bool dummy;
      Item_equal *item_eq;
3179 3180
      //Item *item= (it++)->real_item();
      Item *item= (*(p_item++))->real_item();
3181 3182 3183 3184 3185 3186 3187 3188 3189 3190 3191 3192 3193 3194 3195
      DBUG_ASSERT(item->type() == Item::FIELD_ITEM);
      Field *copy_to= ((Item_field*)item)->field;
      /*
        Tricks with Item_equal are due to the following: suppose we have a
        query:
        
        ... WHERE cond(ot.col) AND ot.col IN (SELECT it2.col FROM it1,it2
                                               WHERE it1.col= it2.col)
         then equality propagation will create an 
         
           Item_equal(it1.col, it2.col, ot.col) 
         
         then substitute_for_best_equal_field() will change the conditions
         according to the join order:

3196 3197 3198 3199 3200
         table | attached condition
         ------+--------------------
          it1  |
          it2  | it1.col=it2.col
          ot   | cond(it1.col)
3201 3202 3203 3204 3205 3206 3207 3208 3209 3210 3211 3212 3213

         although we've originally had "SELECT it2.col", conditions attached 
         to subsequent outer tables will refer to it1.col, so SJM-Scan will
         need to unpack data to there. 
         That is, if an element from subquery's select list participates in 
         equality propagation, then we need to unpack it to the first
         element equality propagation member that refers to table that is
         within the subquery.
      */
      item_eq= find_item_equal(tab->join->cond_equal, copy_to, &dummy);

      if (item_eq)
      {
3214
        List_iterator<Item> it(item_eq->equal_items);
3215 3216 3217
        /* We're interested in field items only */
        if (item_eq->get_const())
          it++;
3218
        Item *item;
3219 3220 3221 3222
        while ((item= it++))
        {
          if (!(item->used_tables() & ~emb_sj_nest->sj_inner_tables))
          {
3223
            DBUG_ASSERT(item->real_item()->type() == Item::FIELD_ITEM);
3224
            copy_to= ((Item_field *) (item->real_item()))->field;
3225 3226 3227 3228 3229 3230 3231 3232
            break;
          }
        }
      }
      sjm->copy_field[i].set(copy_to, sjm->table->field[i], FALSE);
      /* The write_set for source tables must be set up to allow the copying */
      bitmap_set_bit(copy_to->table->write_set, copy_to->field_index);
    }
3233 3234 3235 3236 3237 3238 3239 3240
    sjm_tab->type= JT_ALL;

    /* Initialize full scan */
    sjm_tab->read_first_record= join_read_record_no_init;
    sjm_tab->read_record.copy_field= sjm->copy_field;
    sjm_tab->read_record.copy_field_end= sjm->copy_field +
                                         sjm->sjm_table_cols.elements;
    sjm_tab->read_record.read_record= rr_sequential_and_unpack;
3241 3242
  }

3243 3244
  sjm_tab->bush_children->end[-1].next_select= end_sj_materialize;

3245 3246 3247 3248 3249 3250 3251 3252 3253 3254 3255 3256 3257 3258 3259 3260 3261 3262 3263 3264 3265 3266 3267 3268 3269 3270 3271 3272 3273 3274 3275 3276 3277 3278 3279 3280 3281 3282 3283 3284 3285 3286 3287 3288 3289 3290 3291 3292 3293 3294 3295 3296 3297 3298 3299 3300 3301 3302 3303 3304 3305 3306 3307 3308 3309 3310 3311 3312 3313 3314 3315 3316 3317 3318 3319 3320 3321 3322 3323 3324 3325 3326 3327 3328 3329 3330 3331 3332 3333 3334 3335 3336 3337 3338 3339 3340 3341 3342 3343 3344 3345 3346 3347 3348 3349 3350 3351 3352 3353 3354 3355 3356 3357 3358 3359 3360 3361 3362 3363 3364 3365 3366 3367 3368 3369 3370 3371 3372 3373 3374 3375 3376 3377 3378 3379 3380 3381 3382 3383 3384 3385 3386 3387 3388 3389
  DBUG_RETURN(FALSE);
}



/*
  Create subquery IN-equalities assuming use of materialization strategy
  
  SYNOPSIS
    create_subq_in_equalities()
      thd        Thread handle
      sjm        Semi-join materialization structure
      subq_pred  The subquery predicate

  DESCRIPTION
    Create subquery IN-equality predicates. That is, for a subquery
    
      (oe1, oe2, ...) IN (SELECT ie1, ie2, ... FROM ...)
    
    create "oe1=ie1 AND ie1=ie2 AND ..." expression, such that ie1, ie2, ..
    refer to the columns of the table that's used to materialize the
    subquery.

  RETURN 
    Created condition
*/

static Item *create_subq_in_equalities(THD *thd, SJ_MATERIALIZATION_INFO *sjm, 
                                Item_in_subselect *subq_pred)
{
  Item *res= NULL;
  if (subq_pred->left_expr->cols() == 1)
  {
    if (!(res= new Item_func_eq(subq_pred->left_expr,
                                new Item_field(sjm->table->field[0]))))
      return NULL; /* purecov: inspected */
  }
  else
  {
    Item *conj;
    for (uint i= 0; i < subq_pred->left_expr->cols(); i++)
    {
      if (!(conj= new Item_func_eq(subq_pred->left_expr->element_index(i), 
                                   new Item_field(sjm->table->field[i]))) ||
          !(res= and_items(res, conj)))
        return NULL; /* purecov: inspected */
    }
  }
  if (res->fix_fields(thd, &res))
    return NULL; /* purecov: inspected */
  return res;
}




static void remove_sj_conds(Item **tree)
{
  if (*tree)
  {
    if (is_cond_sj_in_equality(*tree))
    {
      *tree= NULL;
      return;
    }
    else if ((*tree)->type() == Item::COND_ITEM) 
    {
      Item *item;
      List_iterator<Item> li(*(((Item_cond*)*tree)->argument_list()));
      while ((item= li++))
      {
        if (is_cond_sj_in_equality(item))
          li.replace(new Item_int(1));
      }
    }
  }
}

/* Check if given Item was injected by semi-join equality */
static bool is_cond_sj_in_equality(Item *item)
{
  if (item->type() == Item::FUNC_ITEM &&
      ((Item_func*)item)->functype()== Item_func::EQ_FUNC)
  {
    Item_func_eq *item_eq= (Item_func_eq*)item;
    return test(item_eq->in_equality_no != UINT_MAX);
  }
  return FALSE;
}


/*
  Create a temporary table to weed out duplicate rowid combinations

  SYNOPSIS

    create_duplicate_weedout_tmp_table()
      thd                    Thread handle
      uniq_tuple_length_arg  Length of the table's column
      sjtbl                  Update sjtbl->[start_]recinfo values which 
                             will be needed if we'll need to convert the 
                             created temptable from HEAP to MyISAM/Maria.

  DESCRIPTION
    Create a temporary table to weed out duplicate rowid combinations. The
    table has a single column that is a concatenation of all rowids in the
    combination. 

    Depending on the needed length, there are two cases:

    1. When the length of the column < max_key_length:

      CREATE TABLE tmp (col VARBINARY(n) NOT NULL, UNIQUE KEY(col));

    2. Otherwise (not a valid SQL syntax but internally supported):

      CREATE TABLE tmp (col VARBINARY NOT NULL, UNIQUE CONSTRAINT(col));

    The code in this function was produced by extraction of relevant parts
    from create_tmp_table().

  RETURN
    created table
    NULL on error
*/

TABLE *create_duplicate_weedout_tmp_table(THD *thd, 
                                          uint uniq_tuple_length_arg,
                                          SJ_TMP_TABLE *sjtbl)
{
  MEM_ROOT *mem_root_save, own_root;
  TABLE *table;
  TABLE_SHARE *share;
  uint  temp_pool_slot=MY_BIT_NONE;
  char	*tmpname,path[FN_REFLEN];
  Field **reg_field;
  KEY_PART_INFO *key_part_info;
  KEY *keyinfo;
  uchar *group_buff;
  uchar *bitmaps;
  uint *blob_field;
  ENGINE_COLUMNDEF *recinfo, *start_recinfo;
  bool using_unique_constraint=FALSE;
  bool use_packed_rows= FALSE;
  Field *field, *key_field;
3390
  uint null_pack_length, null_count;
3391 3392 3393 3394 3395 3396 3397 3398 3399 3400 3401 3402 3403 3404 3405 3406 3407 3408 3409 3410 3411 3412 3413 3414 3415 3416 3417 3418 3419 3420 3421 3422 3423 3424 3425 3426 3427 3428 3429 3430 3431 3432 3433 3434 3435 3436 3437 3438 3439 3440 3441 3442 3443 3444 3445 3446 3447 3448 3449
  uchar *null_flags;
  uchar *pos;
  DBUG_ENTER("create_duplicate_weedout_tmp_table");
  DBUG_ASSERT(!sjtbl->is_degenerate);
  /*
    STEP 1: Get temporary table name
  */
  statistic_increment(thd->status_var.created_tmp_tables, &LOCK_status);
  if (use_temp_pool && !(test_flags & TEST_KEEP_TMP_TABLES))
    temp_pool_slot = bitmap_lock_set_next(&temp_pool);

  if (temp_pool_slot != MY_BIT_NONE) // we got a slot
    sprintf(path, "%s_%lx_%i", tmp_file_prefix,
	    current_pid, temp_pool_slot);
  else
  {
    /* if we run out of slots or we are not using tempool */
    sprintf(path,"%s%lx_%lx_%x", tmp_file_prefix,current_pid,
            thd->thread_id, thd->tmp_table++);
  }
  fn_format(path, path, mysql_tmpdir, "", MY_REPLACE_EXT|MY_UNPACK_FILENAME);

  /* STEP 2: Figure if we'll be using a key or blob+constraint */
  if (uniq_tuple_length_arg >= CONVERT_IF_BIGGER_TO_BLOB)
    using_unique_constraint= TRUE;

  /* STEP 3: Allocate memory for temptable description */
  init_sql_alloc(&own_root, TABLE_ALLOC_BLOCK_SIZE, 0);
  if (!multi_alloc_root(&own_root,
                        &table, sizeof(*table),
                        &share, sizeof(*share),
                        &reg_field, sizeof(Field*) * (1+1),
                        &blob_field, sizeof(uint)*2,
                        &keyinfo, sizeof(*keyinfo),
                        &key_part_info, sizeof(*key_part_info) * 2,
                        &start_recinfo,
                        sizeof(*recinfo)*(1*2+4),
                        &tmpname, (uint) strlen(path)+1,
                        &group_buff, (!using_unique_constraint ?
                                      uniq_tuple_length_arg : 0),
                        &bitmaps, bitmap_buffer_size(1)*3,
                        NullS))
  {
    if (temp_pool_slot != MY_BIT_NONE)
      bitmap_lock_clear_bit(&temp_pool, temp_pool_slot);
    DBUG_RETURN(NULL);
  }
  strmov(tmpname,path);
  

  /* STEP 4: Create TABLE description */
  bzero((char*) table,sizeof(*table));
  bzero((char*) reg_field,sizeof(Field*)*2);

  table->mem_root= own_root;
  mem_root_save= thd->mem_root;
  thd->mem_root= &table->mem_root;

  table->field=reg_field;
3450 3451
  table->alias.set("weedout-tmp", sizeof("weedout-tmp")-1,
                   table_alias_charset);
3452 3453 3454 3455 3456 3457 3458 3459 3460 3461 3462 3463 3464 3465 3466 3467 3468 3469 3470 3471 3472 3473 3474 3475 3476 3477 3478 3479 3480 3481 3482 3483 3484 3485 3486 3487 3488 3489 3490 3491 3492 3493 3494 3495 3496 3497 3498 3499 3500 3501 3502 3503 3504 3505 3506 3507 3508 3509 3510 3511 3512 3513 3514 3515 3516 3517 3518 3519 3520 3521 3522 3523 3524 3525 3526 3527 3528 3529 3530 3531 3532 3533 3534 3535 3536 3537 3538 3539 3540 3541 3542 3543 3544 3545 3546 3547 3548 3549 3550 3551 3552 3553 3554 3555 3556 3557 3558 3559 3560 3561 3562 3563 3564 3565 3566 3567 3568 3569 3570 3571 3572 3573 3574 3575 3576 3577 3578 3579
  table->reginfo.lock_type=TL_WRITE;	/* Will be updated */
  table->db_stat=HA_OPEN_KEYFILE+HA_OPEN_RNDFILE;
  table->map=1;
  table->temp_pool_slot = temp_pool_slot;
  table->copy_blobs= 1;
  table->in_use= thd;
  table->quick_keys.init();
  table->covering_keys.init();
  table->keys_in_use_for_query.init();

  table->s= share;
  init_tmp_table_share(thd, share, "", 0, tmpname, tmpname);
  share->blob_field= blob_field;
  share->blob_ptr_size= portable_sizeof_char_ptr;
  share->table_charset= NULL;
  share->primary_key= MAX_KEY;               // Indicate no primary key
  share->keys_for_keyread.init();
  share->keys_in_use.init();

  /* Create the field */
  {
    /*
      For the sake of uniformity, always use Field_varstring (altough we could
      use Field_string for shorter keys)
    */
    field= new Field_varstring(uniq_tuple_length_arg, FALSE, "rowids", share,
                               &my_charset_bin);
    if (!field)
      DBUG_RETURN(0);
    field->table= table;
    field->key_start.init(0);
    field->part_of_key.init(0);
    field->part_of_sortkey.init(0);
    field->unireg_check= Field::NONE;
    field->flags= (NOT_NULL_FLAG | BINARY_FLAG | NO_DEFAULT_VALUE_FLAG);
    field->reset_fields();
    field->init(table);
    field->orig_table= NULL;
     
    field->field_index= 0;
    
    *(reg_field++)= field;
    *blob_field= 0;
    *reg_field= 0;

    share->fields= 1;
    share->blob_fields= 0;
  }

  uint reclength= field->pack_length();
  if (using_unique_constraint)
  { 
    share->db_plugin= ha_lock_engine(0, TMP_ENGINE_HTON);
    table->file= get_new_handler(share, &table->mem_root,
                                 share->db_type());
    DBUG_ASSERT(uniq_tuple_length_arg <= table->file->max_key_length());
  }
  else
  {
    share->db_plugin= ha_lock_engine(0, heap_hton);
    table->file= get_new_handler(share, &table->mem_root,
                                 share->db_type());
  }
  if (!table->file)
    goto err;

  null_count=1;
  
  null_pack_length= 1;
  reclength += null_pack_length;

  share->reclength= reclength;
  {
    uint alloc_length=ALIGN_SIZE(share->reclength + MI_UNIQUE_HASH_LENGTH+1);
    share->rec_buff_length= alloc_length;
    if (!(table->record[0]= (uchar*)
                            alloc_root(&table->mem_root, alloc_length*3)))
      goto err;
    table->record[1]= table->record[0]+alloc_length;
    share->default_values= table->record[1]+alloc_length;
  }
  setup_tmp_table_column_bitmaps(table, bitmaps);

  recinfo= start_recinfo;
  null_flags=(uchar*) table->record[0];
  pos=table->record[0]+ null_pack_length;
  if (null_pack_length)
  {
    bzero((uchar*) recinfo,sizeof(*recinfo));
    recinfo->type=FIELD_NORMAL;
    recinfo->length=null_pack_length;
    recinfo++;
    bfill(null_flags,null_pack_length,255);	// Set null fields

    table->null_flags= (uchar*) table->record[0];
    share->null_fields= null_count;
    share->null_bytes= null_pack_length;
  }
  null_count=1;

  {
    //Field *field= *reg_field;
    uint length;
    bzero((uchar*) recinfo,sizeof(*recinfo));
    field->move_field(pos,(uchar*) 0,0);

    field->reset();
    /*
      Test if there is a default field value. The test for ->ptr is to skip
      'offset' fields generated by initalize_tables
    */
    // Initialize the table field:
    bzero(field->ptr, field->pack_length());

    length=field->pack_length();
    pos+= length;

    /* Make entry for create table */
    recinfo->length=length;
    if (field->flags & BLOB_FLAG)
      recinfo->type= FIELD_BLOB;
    else if (use_packed_rows &&
             field->real_type() == MYSQL_TYPE_STRING &&
	     length >= MIN_STRING_LENGTH_TO_PACK_ROWS)
      recinfo->type=FIELD_SKIP_ENDSPACE;
    else
      recinfo->type=FIELD_NORMAL;

3580
    field->set_table_name(&table->alias);
3581 3582 3583 3584 3585 3586 3587 3588 3589 3590 3591 3592 3593 3594 3595 3596 3597 3598 3599 3600 3601 3602 3603 3604 3605 3606 3607 3608 3609 3610 3611 3612 3613 3614 3615 3616 3617 3618 3619 3620 3621 3622 3623 3624 3625 3626 3627
  }

  if (thd->variables.tmp_table_size == ~ (ulonglong) 0)		// No limit
    share->max_rows= ~(ha_rows) 0;
  else
    share->max_rows= (ha_rows) (((share->db_type() == heap_hton) ?
                                 min(thd->variables.tmp_table_size,
                                     thd->variables.max_heap_table_size) :
                                 thd->variables.tmp_table_size) /
			         share->reclength);
  set_if_bigger(share->max_rows,1);		// For dummy start options


  //// keyinfo= param->keyinfo;
  if (TRUE)
  {
    DBUG_PRINT("info",("Creating group key in temporary table"));
    share->keys=1;
    share->uniques= test(using_unique_constraint);
    table->key_info=keyinfo;
    keyinfo->key_part=key_part_info;
    keyinfo->flags=HA_NOSAME;
    keyinfo->usable_key_parts= keyinfo->key_parts= 1;
    keyinfo->key_length=0;
    keyinfo->rec_per_key=0;
    keyinfo->algorithm= HA_KEY_ALG_UNDEF;
    keyinfo->name= (char*) "weedout_key";
    {
      key_part_info->null_bit=0;
      key_part_info->field=  field;
      key_part_info->offset= field->offset(table->record[0]);
      key_part_info->length= (uint16) field->key_length();
      key_part_info->type=   (uint8) field->key_type();
      key_part_info->key_type = FIELDFLAG_BINARY;
      if (!using_unique_constraint)
      {
	if (!(key_field= field->new_key_field(thd->mem_root, table,
                                              group_buff,
                                              field->null_ptr,
                                              field->null_bit)))
	  goto err;
        key_part_info->key_part_flag|= HA_END_SPACE_ARE_EQUAL; //todo need this?
      }
      keyinfo->key_length+=  key_part_info->length;
    }
  }

3628
  if (thd->is_fatal_error)			// If end of memory
3629 3630
    goto err;
  share->db_record_offset= 1;
3631 3632 3633 3634
  table->no_rows= 1;              		// We don't need the data

  // recinfo must point after last field
  recinfo++;
3635 3636 3637 3638 3639 3640 3641 3642 3643 3644 3645 3646 3647 3648 3649 3650 3651 3652 3653 3654 3655 3656 3657 3658 3659 3660 3661 3662 3663 3664 3665 3666 3667 3668 3669 3670 3671 3672 3673 3674 3675 3676 3677 3678 3679 3680 3681 3682 3683 3684 3685 3686 3687 3688 3689 3690 3691 3692 3693 3694 3695 3696 3697 3698 3699 3700 3701 3702 3703 3704 3705 3706 3707 3708 3709 3710 3711 3712 3713 3714 3715 3716 3717 3718 3719 3720 3721 3722 3723 3724 3725 3726
  if (share->db_type() == TMP_ENGINE_HTON)
  {
    if (create_internal_tmp_table(table, keyinfo, start_recinfo, &recinfo, 0))
      goto err;
  }
  sjtbl->start_recinfo= start_recinfo;
  sjtbl->recinfo=       recinfo;
  if (open_tmp_table(table))
    goto err;

  thd->mem_root= mem_root_save;
  DBUG_RETURN(table);

err:
  thd->mem_root= mem_root_save;
  free_tmp_table(thd,table);                    /* purecov: inspected */
  if (temp_pool_slot != MY_BIT_NONE)
    bitmap_lock_clear_bit(&temp_pool, temp_pool_slot);
  DBUG_RETURN(NULL);				/* purecov: inspected */
}


/*
  SemiJoinDuplicateElimination: Reset the temporary table
*/

int do_sj_reset(SJ_TMP_TABLE *sj_tbl)
{
  DBUG_ENTER("do_sj_reset");
  if (sj_tbl->tmp_table)
  {
    int rc= sj_tbl->tmp_table->file->ha_delete_all_rows();
    DBUG_RETURN(rc);
  }
  sj_tbl->have_degenerate_row= FALSE;
  DBUG_RETURN(0);
}

/*
  SemiJoinDuplicateElimination: Weed out duplicate row combinations

  SYNPOSIS
    do_sj_dups_weedout()
      thd    Thread handle
      sjtbl  Duplicate weedout table

  DESCRIPTION
    Try storing current record combination of outer tables (i.e. their
    rowids) in the temporary table. This records the fact that we've seen 
    this record combination and also tells us if we've seen it before.

  RETURN
    -1  Error
    1   The row combination is a duplicate (discard it)
    0   The row combination is not a duplicate (continue)
*/

int do_sj_dups_weedout(THD *thd, SJ_TMP_TABLE *sjtbl) 
{
  int error;
  SJ_TMP_TABLE::TAB *tab= sjtbl->tabs;
  SJ_TMP_TABLE::TAB *tab_end= sjtbl->tabs_end;
  uchar *ptr;
  uchar *nulls_ptr;

  DBUG_ENTER("do_sj_dups_weedout");

  if (sjtbl->is_degenerate)
  {
    if (sjtbl->have_degenerate_row) 
      DBUG_RETURN(1);

    sjtbl->have_degenerate_row= TRUE;
    DBUG_RETURN(0);
  }

  ptr= sjtbl->tmp_table->record[0] + 1;

  /* Put the the rowids tuple into table->record[0]: */

  // 1. Store the length 
  if (((Field_varstring*)(sjtbl->tmp_table->field[0]))->length_bytes == 1)
  {
    *ptr= (uchar)(sjtbl->rowid_len + sjtbl->null_bytes);
    ptr++;
  }
  else
  {
    int2store(ptr, sjtbl->rowid_len + sjtbl->null_bytes);
    ptr += 2;
  }

3727
  nulls_ptr= ptr;
3728 3729 3730 3731 3732 3733 3734 3735 3736 3737 3738 3739 3740 3741 3742 3743 3744 3745 3746 3747 3748 3749 3750 3751
  // 2. Zero the null bytes 
  if (sjtbl->null_bytes)
  {
    bzero(ptr, sjtbl->null_bytes);
    ptr += sjtbl->null_bytes; 
  }

  // 3. Put the rowids
  for (uint i=0; tab != tab_end; tab++, i++)
  {
    handler *h= tab->join_tab->table->file;
    if (tab->join_tab->table->maybe_null && tab->join_tab->table->null_row)
    {
      /* It's a NULL-complemented row */
      *(nulls_ptr + tab->null_byte) |= tab->null_bit;
      bzero(ptr + tab->rowid_offset, h->ref_length);
    }
    else
    {
      /* Copy the rowid value */
      memcpy(ptr + tab->rowid_offset, h->ref, h->ref_length);
    }
  }

3752
  error= sjtbl->tmp_table->file->ha_write_tmp_row(sjtbl->tmp_table->record[0]);
3753 3754 3755 3756 3757 3758 3759 3760 3761 3762 3763 3764 3765 3766 3767 3768 3769 3770 3771 3772 3773 3774 3775 3776 3777 3778 3779 3780 3781 3782 3783 3784 3785 3786 3787 3788 3789 3790 3791 3792 3793 3794 3795 3796 3797 3798 3799 3800 3801 3802 3803 3804 3805 3806 3807 3808 3809 3810 3811 3812 3813 3814 3815 3816 3817 3818 3819 3820 3821 3822 3823 3824 3825 3826 3827 3828 3829 3830 3831 3832 3833 3834 3835 3836 3837 3838 3839 3840 3841 3842 3843 3844 3845 3846 3847 3848 3849 3850 3851 3852 3853 3854 3855 3856 3857 3858 3859 3860 3861 3862 3863 3864 3865 3866 3867 3868
  if (error)
  {
    /* create_internal_tmp_table_from_heap will generate error if needed */
    if (!sjtbl->tmp_table->file->is_fatal_error(error, HA_CHECK_DUP))
      DBUG_RETURN(1); /* Duplicate */
    if (create_internal_tmp_table_from_heap(thd, sjtbl->tmp_table,
                                            sjtbl->start_recinfo,
                                            &sjtbl->recinfo, error, 1))
      DBUG_RETURN(-1);
  }
  DBUG_RETURN(0);
}


/*
  Setup the strategies to eliminate semi-join duplicates.
  
  SYNOPSIS
    setup_semijoin_dups_elimination()
      join           Join to process
      options        Join options (needed to see if join buffering will be 
                     used or not)
      no_jbuf_after  Another bit of information re where join buffering will
                     be used.

  DESCRIPTION
    Setup the strategies to eliminate semi-join duplicates. ATM there are 4
    strategies:

    1. DuplicateWeedout (use of temptable to remove duplicates based on rowids
                         of row combinations)
    2. FirstMatch (pick only the 1st matching row combination of inner tables)
    3. LooseScan (scanning the sj-inner table in a way that groups duplicates
                  together and picking the 1st one)
    4. SJ-Materialization.
    
    The join order has "duplicate-generating ranges", and every range is
    served by one strategy or a combination of FirstMatch with with some
    other strategy.
    
    "Duplicate-generating range" is defined as a range within the join order
    that contains all of the inner tables of a semi-join. All ranges must be
    disjoint, if tables of several semi-joins are interleaved, then the ranges
    are joined together, which is equivalent to converting
      SELECT ... WHERE oe1 IN (SELECT ie1 ...) AND oe2 IN (SELECT ie2 )
    to
      SELECT ... WHERE (oe1, oe2) IN (SELECT ie1, ie2 ... ...)
    .

    Applicability conditions are as follows:

    DuplicateWeedout strategy
    ~~~~~~~~~~~~~~~~~~~~~~~~~

      (ot|nt)*  [ it ((it|ot|nt)* (it|ot))]  (nt)*
      +------+  +=========================+  +---+
        (1)                 (2)               (3)

       (1) - Prefix of OuterTables (those that participate in 
             IN-equality and/or are correlated with subquery) and outer 
             Non-correlated tables.
       (2) - The handled range. The range starts with the first sj-inner
             table, and covers all sj-inner and outer tables 
             Within the range,  Inner, Outer, outer non-correlated tables
             may follow in any order.
       (3) - The suffix of outer non-correlated tables.
    
    FirstMatch strategy
    ~~~~~~~~~~~~~~~~~~~

      (ot|nt)*  [ it ((it|nt)* it) ]  (nt)*
      +------+  +==================+  +---+
        (1)             (2)          (3)

      (1) - Prefix of outer and non-correlated tables
      (2) - The handled range, which may contain only inner and
            non-correlated tables.
      (3) - The suffix of outer non-correlated tables.

    LooseScan strategy 
    ~~~~~~~~~~~~~~~~~~

     (ot|ct|nt) [ loosescan_tbl (ot|nt|it)* it ]  (ot|nt)*
     +--------+   +===========+ +=============+   +------+
        (1)           (2)          (3)              (4)
     
      (1) - Prefix that may contain any outer tables. The prefix must contain
            all the non-trivially correlated outer tables. (non-trivially means
            that the correlation is not just through the IN-equality).
      
      (2) - Inner table for which the LooseScan scan is performed.

      (3) - The remainder of the duplicate-generating range. It is served by 
            application of FirstMatch strategy, with the exception that
            outer IN-correlated tables are considered to be non-correlated.

      (4) - THe suffix of outer and outer non-correlated tables.

  
  The choice between the strategies is made by the join optimizer (see
  advance_sj_state() and fix_semijoin_strategies_for_picked_join_order()).
  This function sets up all fields/structures/etc needed for execution except
  for setup/initialization of semi-join materialization which is done in 
  setup_sj_materialization() (todo: can't we move that to here also?)

  RETURN
    FALSE  OK 
    TRUE   Out of memory error
*/

int setup_semijoin_dups_elimination(JOIN *join, ulonglong options, 
                                    uint no_jbuf_after)
{
  uint i;
  THD *thd= join->thd;
  DBUG_ENTER("setup_semijoin_dups_elimination");
3869 3870
  
  POSITION *pos= join->best_positions + join->const_tables;
3871
  for (i= join->const_tables ; i < join->top_join_tab_count; )
3872 3873
  {
    JOIN_TAB *tab=join->join_tab + i;
3874
    //POSITION *pos= join->best_positions + i;
3875 3876 3877 3878 3879
    uint keylen, keyno;
    switch (pos->sj_strategy) {
      case SJ_OPT_MATERIALIZE:
      case SJ_OPT_MATERIALIZE_SCAN:
        /* Do nothing */
3880 3881
        i+= 1;// It used to be pos->n_sj_tables, but now they are embedded in a nest
        pos += pos->n_sj_tables;
3882 3883 3884 3885 3886
        break;
      case SJ_OPT_LOOSE_SCAN:
      {
        /* We jump from the last table to the first one */
        tab->loosescan_match_tab= tab + pos->n_sj_tables - 1;
3887
        for (uint j= i; j < i + pos->n_sj_tables; j++)
3888
          join->join_tab[j].inside_loosescan_range= TRUE;
3889 3890 3891 3892 3893 3894 3895 3896 3897 3898

        /* Calculate key length */
        keylen= 0;
        keyno= pos->loosescan_key;
        for (uint kp=0; kp < pos->loosescan_parts; kp++)
          keylen += tab->table->key_info[keyno].key_part[kp].store_length;

        tab->loosescan_key_len= keylen;
        if (pos->n_sj_tables > 1) 
          tab[pos->n_sj_tables - 1].do_firstmatch= tab;
Sergey Petrunya's avatar
Sergey Petrunya committed
3899
        i+= pos->n_sj_tables;
3900
        pos+= pos->n_sj_tables;
3901 3902 3903 3904 3905 3906 3907 3908 3909
        break;
      }
      case SJ_OPT_DUPS_WEEDOUT:
      {
        /*
          Check for join buffering. If there is one, move the first table
          forwards, but do not destroy other duplicate elimination methods.
        */
        uint first_table= i;
3910
        uint join_cache_level= join->thd->variables.join_cache_level;
3911 3912
        for (uint j= i; j < i + pos->n_sj_tables; j++)
        {
3913 3914 3915 3916 3917 3918 3919 3920 3921 3922 3923
          /*
            When we'll properly take join buffering into account during
            join optimization, the below check should be changed to 
            "if (join->best_positions[j].use_join_buffer && 
                 j <= no_jbuf_after)".
            For now, use a rough criteria:
          */
          JOIN_TAB *js_tab=join->join_tab + j; 
          if (j != join->const_tables && js_tab->use_quick != 2 &&
              j <= no_jbuf_after &&
              ((js_tab->type == JT_ALL && join_cache_level != 0) ||
Igor Babaev's avatar
Igor Babaev committed
3924 3925
               (join_cache_level > 2 && (js_tab->type == JT_REF || 
                                         js_tab->type == JT_EQ_REF))))
3926
          {
3927
            /* Looks like we'll be using join buffer */
3928 3929 3930 3931 3932 3933 3934 3935 3936 3937 3938 3939 3940 3941 3942 3943 3944 3945 3946 3947 3948 3949 3950 3951 3952 3953 3954 3955 3956 3957 3958 3959 3960 3961 3962 3963
            first_table= join->const_tables;
            break;
          }
        }

        SJ_TMP_TABLE::TAB sjtabs[MAX_TABLES];
        SJ_TMP_TABLE::TAB *last_tab= sjtabs;
        uint jt_rowid_offset= 0; // # tuple bytes are already occupied (w/o NULL bytes)
        uint jt_null_bits= 0;    // # null bits in tuple bytes
        /*
          Walk through the range and remember
           - tables that need their rowids to be put into temptable
           - the last outer table
        */
        for (JOIN_TAB *j=join->join_tab + first_table; 
             j < join->join_tab + i + pos->n_sj_tables; j++)
        {
          if (sj_table_is_included(join, j))
          {
            last_tab->join_tab= j;
            last_tab->rowid_offset= jt_rowid_offset;
            jt_rowid_offset += j->table->file->ref_length;
            if (j->table->maybe_null)
            {
              last_tab->null_byte= jt_null_bits / 8;
              last_tab->null_bit= jt_null_bits++;
            }
            last_tab++;
            j->table->prepare_for_position();
            j->keep_current_rowid= TRUE;
          }
        }

        SJ_TMP_TABLE *sjtbl;
        if (jt_rowid_offset) /* Temptable has at least one rowid */
        {
Sergey Petrunya's avatar
Sergey Petrunya committed
3964
          size_t tabs_size= (last_tab - sjtabs) * sizeof(SJ_TMP_TABLE::TAB);
3965 3966 3967 3968 3969 3970 3971 3972 3973 3974 3975 3976 3977 3978 3979 3980 3981 3982 3983 3984 3985 3986 3987 3988 3989 3990 3991 3992 3993 3994 3995 3996
          if (!(sjtbl= (SJ_TMP_TABLE*)thd->alloc(sizeof(SJ_TMP_TABLE))) ||
              !(sjtbl->tabs= (SJ_TMP_TABLE::TAB*) thd->alloc(tabs_size)))
            DBUG_RETURN(TRUE); /* purecov: inspected */
          memcpy(sjtbl->tabs, sjtabs, tabs_size);
          sjtbl->is_degenerate= FALSE;
          sjtbl->tabs_end= sjtbl->tabs + (last_tab - sjtabs);
          sjtbl->rowid_len= jt_rowid_offset;
          sjtbl->null_bits= jt_null_bits;
          sjtbl->null_bytes= (jt_null_bits + 7)/8;
          sjtbl->tmp_table= 
            create_duplicate_weedout_tmp_table(thd, 
                                               sjtbl->rowid_len + 
                                               sjtbl->null_bytes,
                                               sjtbl);
          join->sj_tmp_tables.push_back(sjtbl->tmp_table);
        }
        else
        {
          /* 
            This is a special case where the entire subquery predicate does 
            not depend on anything at all, ie this is 
              WHERE const IN (uncorrelated select)
          */
          if (!(sjtbl= (SJ_TMP_TABLE*)thd->alloc(sizeof(SJ_TMP_TABLE))))
            DBUG_RETURN(TRUE); /* purecov: inspected */
          sjtbl->tmp_table= NULL;
          sjtbl->is_degenerate= TRUE;
          sjtbl->have_degenerate_row= FALSE;
        }
        join->join_tab[first_table].flush_weedout_table= sjtbl;
        join->join_tab[i + pos->n_sj_tables - 1].check_weed_out_table= sjtbl;

Sergey Petrunya's avatar
Sergey Petrunya committed
3997
        i+= pos->n_sj_tables;
3998
        pos+= pos->n_sj_tables;
3999 4000 4001 4002 4003 4004 4005
        break;
      }
      case SJ_OPT_FIRST_MATCH:
      {
        JOIN_TAB *j, *jump_to= tab-1;
        for (j= tab; j != tab + pos->n_sj_tables; j++)
        {
4006 4007 4008 4009 4010 4011
          /*
            NOTE: this loop probably doesn't do the right thing for the case 
            where FirstMatch's duplicate-generating range is interleaved with
            "unrelated" tables (as specified in WL#3750, section 2.2).
          */
          if (!j->emb_sj_nest)
4012 4013 4014 4015 4016 4017 4018 4019
            jump_to= tab;
          else
          {
            j->first_sj_inner_tab= tab;
            j->last_sj_inner_tab= tab + pos->n_sj_tables - 1;
          }
        }
        j[-1].do_firstmatch= jump_to;
Sergey Petrunya's avatar
Sergey Petrunya committed
4020
        i+= pos->n_sj_tables;
4021
        pos+= pos->n_sj_tables;
4022 4023 4024
        break;
      }
      case SJ_OPT_NONE:
Sergey Petrunya's avatar
Sergey Petrunya committed
4025
        i++;
4026
        pos++;
4027 4028 4029 4030 4031 4032 4033 4034 4035 4036 4037 4038 4039 4040 4041 4042 4043 4044 4045 4046 4047 4048 4049 4050 4051 4052 4053 4054 4055 4056 4057 4058 4059 4060 4061 4062 4063 4064 4065 4066 4067 4068 4069 4070 4071 4072 4073 4074 4075 4076 4077
        break;
    }
  }
  DBUG_RETURN(FALSE);
}


/*
  Destroy all temporary tables created by NL-semijoin runtime
*/

void destroy_sj_tmp_tables(JOIN *join)
{
  List_iterator<TABLE> it(join->sj_tmp_tables);
  TABLE *table;
  while ((table= it++))
  {
    /* 
      SJ-Materialization tables are initialized for either sequential reading 
      or index lookup, DuplicateWeedout tables are not initialized for read 
      (we only write to them), so need to call ha_index_or_rnd_end.
    */
    table->file->ha_index_or_rnd_end();
    free_tmp_table(join->thd, table);
  }
  join->sj_tmp_tables.empty();
  join->sjm_info_list.empty();
}


/*
  Remove all records from all temp tables used by NL-semijoin runtime

  SYNOPSIS
    clear_sj_tmp_tables()
      join  The join to remove tables for

  DESCRIPTION
    Remove all records from all temp tables used by NL-semijoin runtime. This 
    must be done before every join re-execution.
*/

int clear_sj_tmp_tables(JOIN *join)
{
  int res;
  List_iterator<TABLE> it(join->sj_tmp_tables);
  TABLE *table;
  while ((table= it++))
  {
    if ((res= table->file->ha_delete_all_rows()))
      return res; /* purecov: inspected */
unknown's avatar
unknown committed
4078 4079
   free_io_cache(table);
   filesort_free_buffers(table,0);
4080 4081 4082 4083 4084 4085 4086 4087 4088 4089 4090 4091 4092 4093 4094 4095 4096 4097 4098 4099 4100 4101 4102 4103 4104 4105 4106 4107 4108 4109 4110 4111 4112 4113 4114 4115 4116 4117 4118 4119 4120 4121 4122 4123 4124 4125 4126 4127 4128 4129 4130 4131 4132 4133 4134 4135 4136 4137 4138 4139 4140 4141 4142 4143 4144 4145 4146 4147 4148 4149 4150 4151 4152 4153 4154 4155 4156 4157 4158 4159 4160 4161 4162 4163 4164 4165 4166 4167 4168 4169 4170 4171 4172 4173 4174 4175 4176 4177 4178 4179 4180 4181 4182 4183 4184 4185 4186 4187 4188 4189 4190 4191 4192 4193 4194 4195 4196 4197 4198 4199 4200 4201 4202 4203 4204 4205 4206 4207 4208
  }

  SJ_MATERIALIZATION_INFO *sjm;
  List_iterator<SJ_MATERIALIZATION_INFO> it2(join->sjm_info_list);
  while ((sjm= it2++))
  {
    sjm->materialized= FALSE;
  }
  return 0;
}


/*
  Check if the table's rowid is included in the temptable

  SYNOPSIS
    sj_table_is_included()
      join      The join
      join_tab  The table to be checked

  DESCRIPTION
    SemiJoinDuplicateElimination: check the table's rowid should be included
    in the temptable. This is so if

    1. The table is not embedded within some semi-join nest
    2. The has been pulled out of a semi-join nest, or

    3. The table is functionally dependent on some previous table

    [4. This is also true for constant tables that can't be
        NULL-complemented but this function is not called for such tables]

  RETURN
    TRUE  - Include table's rowid
    FALSE - Don't
*/

static bool sj_table_is_included(JOIN *join, JOIN_TAB *join_tab)
{
  if (join_tab->emb_sj_nest)
    return FALSE;
  
  /* Check if this table is functionally dependent on the tables that
     are within the same outer join nest
  */
  TABLE_LIST *embedding= join_tab->table->pos_in_table_list->embedding;
  if (join_tab->type == JT_EQ_REF)
  {
    table_map depends_on= 0;
    uint idx;

    for (uint kp= 0; kp < join_tab->ref.key_parts; kp++)
      depends_on |= join_tab->ref.items[kp]->used_tables();

    Table_map_iterator it(depends_on & ~PSEUDO_TABLE_BITS);
    while ((idx= it.next_bit())!=Table_map_iterator::BITMAP_END)
    {
      JOIN_TAB *ref_tab= join->map2table[idx];
      if (embedding != ref_tab->table->pos_in_table_list->embedding)
        return TRUE;
    }
    /* Ok, functionally dependent */
    return FALSE;
  }
  /* Not functionally dependent => need to include*/
  return TRUE;
}


/*
  Index lookup-based subquery: save some flags for EXPLAIN output

  SYNOPSIS
    save_index_subquery_explain_info()
      join_tab  Subquery's join tab (there is only one as index lookup is
                only used for subqueries that are single-table SELECTs)
      where     Subquery's WHERE clause

  DESCRIPTION
    For index lookup-based subquery (i.e. one executed with
    subselect_uniquesubquery_engine or subselect_indexsubquery_engine),
    check its EXPLAIN output row should contain 
      "Using index" (TAB_INFO_FULL_SCAN_ON_NULL) 
      "Using Where" (TAB_INFO_USING_WHERE)
      "Full scan on NULL key" (TAB_INFO_FULL_SCAN_ON_NULL)
    and set appropriate flags in join_tab->packed_info.
*/

static void save_index_subquery_explain_info(JOIN_TAB *join_tab, Item* where)
{
  join_tab->packed_info= TAB_INFO_HAVE_VALUE;
  if (join_tab->table->covering_keys.is_set(join_tab->ref.key))
    join_tab->packed_info |= TAB_INFO_USING_INDEX;
  if (where)
    join_tab->packed_info |= TAB_INFO_USING_WHERE;
  for (uint i = 0; i < join_tab->ref.key_parts; i++)
  {
    if (join_tab->ref.cond_guards[i])
    {
      join_tab->packed_info |= TAB_INFO_FULL_SCAN_ON_NULL;
      break;
    }
  }
}


/*
  Check if the join can be rewritten to [unique_]indexsubquery_engine

  DESCRIPTION
    Check if the join can be changed into [unique_]indexsubquery_engine.

    The check is done after join optimization, the idea is that if the join
    has only one table and uses a [eq_]ref access generated from subselect's
    IN-equality then we replace it with a subselect_indexsubquery_engine or a
    subselect_uniquesubquery_engine.

  RETURN 
    0 - Ok, rewrite done (stop join optimization and return)
    1 - Fatal error (stop join optimization and return)
   -1 - No rewrite performed, continue with join optimization
*/

int rewrite_to_index_subquery_engine(JOIN *join)
{
  THD *thd= join->thd;
  JOIN_TAB* join_tab=join->join_tab;
  SELECT_LEX_UNIT *unit= join->unit;
  DBUG_ENTER("rewrite_to_index_subquery_engine");
4209

4210 4211 4212
  /*
    is this simple IN subquery?
  */
4213 4214 4215 4216 4217 4218 4219 4220 4221 4222 4223 4224 4225
  /* TODO: In order to use these more efficient subquery engines in more cases,
     the following problems need to be solved:
     - the code that removes GROUP BY (group_list), also adds an ORDER BY
       (order), thus GROUP BY queries (almost?) never pass through this branch.
       Solution: remove the test below '!join->order', because we remove the
       ORDER clase for subqueries anyway.
     - in order to set a more efficient engine, the optimizer needs to both
       decide to remove GROUP BY, *and* select one of the JT_[EQ_]REF[_OR_NULL]
       access methods, *and* loose scan should be more expensive or
       inapliccable. When is that possible?
     - Consider expanding the applicability of this rewrite for loose scan
       for group by queries.
  */
4226 4227 4228
  if (!join->group_list && !join->order &&
      join->unit->item && 
      join->unit->item->substype() == Item_subselect::IN_SUBS &&
4229
      join->table_count == 1 && join->conds &&
4230 4231 4232 4233 4234 4235 4236 4237 4238 4239 4240 4241 4242 4243 4244 4245 4246 4247 4248 4249 4250 4251 4252 4253 4254 4255 4256 4257 4258 4259 4260 4261 4262 4263 4264 4265 4266 4267 4268 4269 4270 4271 4272 4273 4274 4275 4276 4277 4278 4279 4280 4281 4282 4283 4284 4285 4286 4287 4288 4289 4290 4291 4292 4293 4294 4295 4296 4297 4298 4299 4300 4301 4302 4303 4304 4305 4306 4307 4308 4309 4310 4311 4312 4313 4314 4315 4316 4317 4318 4319 4320 4321 4322 4323 4324 4325 4326 4327 4328 4329 4330 4331 4332 4333 4334 4335 4336 4337 4338 4339 4340 4341 4342 4343 4344 4345 4346 4347 4348 4349 4350 4351 4352 4353 4354 4355 4356 4357 4358 4359 4360 4361 4362 4363 4364 4365
      !join->unit->is_union())
  {
    if (!join->having)
    {
      Item *where= join->conds;
      if (join_tab[0].type == JT_EQ_REF &&
	  join_tab[0].ref.items[0]->name == in_left_expr_name)
      {
        remove_subq_pushed_predicates(join, &where);
        save_index_subquery_explain_info(join_tab, where);
        join_tab[0].type= JT_UNIQUE_SUBQUERY;
        join->error= 0;
        DBUG_RETURN(unit->item->
                    change_engine(new
                                  subselect_uniquesubquery_engine(thd,
                                                                  join_tab,
                                                                  unit->item,
                                                                  where)));
      }
      else if (join_tab[0].type == JT_REF &&
	       join_tab[0].ref.items[0]->name == in_left_expr_name)
      {
	remove_subq_pushed_predicates(join, &where);
        save_index_subquery_explain_info(join_tab, where);
        join_tab[0].type= JT_INDEX_SUBQUERY;
        join->error= 0;
        DBUG_RETURN(unit->item->
                    change_engine(new
                                  subselect_indexsubquery_engine(thd,
                                                                 join_tab,
                                                                 unit->item,
                                                                 where,
                                                                 NULL,
                                                                 0)));
      }
    } else if (join_tab[0].type == JT_REF_OR_NULL &&
	       join_tab[0].ref.items[0]->name == in_left_expr_name &&
               join->having->name == in_having_cond)
    {
      join_tab[0].type= JT_INDEX_SUBQUERY;
      join->error= 0;
      join->conds= remove_additional_cond(join->conds);
      save_index_subquery_explain_info(join_tab, join->conds);
      DBUG_RETURN(unit->item->
		  change_engine(new subselect_indexsubquery_engine(thd,
								   join_tab,
								   unit->item,
								   join->conds,
                                                                   join->having,
								   1)));
    }
  }

  DBUG_RETURN(-1); /* Haven't done the rewrite */
}


/**
  Remove additional condition inserted by IN/ALL/ANY transformation.

  @param conds   condition for processing

  @return
    new conditions
*/

static Item *remove_additional_cond(Item* conds)
{
  if (conds->name == in_additional_cond)
    return 0;
  if (conds->type() == Item::COND_ITEM)
  {
    Item_cond *cnd= (Item_cond*) conds;
    List_iterator<Item> li(*(cnd->argument_list()));
    Item *item;
    while ((item= li++))
    {
      if (item->name == in_additional_cond)
      {
	li.remove();
	if (cnd->argument_list()->elements == 1)
	  return cnd->argument_list()->head();
	return conds;
      }
    }
  }
  return conds;
}


/*
  Remove the predicates pushed down into the subquery

  SYNOPSIS
    remove_subq_pushed_predicates()
      where   IN  Must be NULL
              OUT The remaining WHERE condition, or NULL

  DESCRIPTION
    Given that this join will be executed using (unique|index)_subquery,
    without "checking NULL", remove the predicates that were pushed down
    into the subquery.

    If the subquery compares scalar values, we can remove the condition that
    was wrapped into trig_cond (it will be checked when needed by the subquery
    engine)

    If the subquery compares row values, we need to keep the wrapped
    equalities in the WHERE clause: when the left (outer) tuple has both NULL
    and non-NULL values, we'll do a full table scan and will rely on the
    equalities corresponding to non-NULL parts of left tuple to filter out
    non-matching records.

    TODO: We can remove the equalities that will be guaranteed to be true by the
    fact that subquery engine will be using index lookup. This must be done only
    for cases where there are no conversion errors of significance, e.g. 257
    that is searched in a byte. But this requires homogenization of the return 
    codes of all Field*::store() methods.
*/

static void remove_subq_pushed_predicates(JOIN *join, Item **where)
{
  if (join->conds->type() == Item::FUNC_ITEM &&
      ((Item_func *)join->conds)->functype() == Item_func::EQ_FUNC &&
      ((Item_func *)join->conds)->arguments()[0]->type() == Item::REF_ITEM &&
      ((Item_func *)join->conds)->arguments()[1]->type() == Item::FIELD_ITEM &&
      test_if_ref (join->conds,
                   (Item_field *)((Item_func *)join->conds)->arguments()[1],
                   ((Item_func *)join->conds)->arguments()[0]))
  {
    *where= 0;
    return;
  }
}


Sergey Petrunya's avatar
Sergey Petrunya committed
4366 4367


4368
/**
4369
  Optimize all subqueries of a query that were not flattened into a semijoin.
4370

4371 4372
  @details
  Optimize all immediate children subqueries of a query.
4373 4374 4375 4376 4377 4378 4379 4380 4381 4382 4383 4384 4385 4386 4387 4388 4389

  This phase must be called after substitute_for_best_equal_field() because
  that function may replace items with other items from a multiple equality,
  and we need to reference the correct items in the index access method of the
  IN predicate.

  @return Operation status
  @retval FALSE     success.
  @retval TRUE      error occurred.
*/

bool JOIN::optimize_unflattened_subqueries()
{
  return select_lex->optimize_unflattened_subqueries();
}


4390
/*
4391 4392 4393 4394 4395
  Join tab execution startup function.

  SYNOPSIS
    join_tab_execution_startup()
      tab  Join tab to perform startup actions for
4396 4397 4398 4399 4400 4401 4402 4403 4404

  DESCRIPTION
    Join tab execution startup function. This is different from
    tab->read_first_record in the regard that this has actions that are to be
    done once per join execution.

    Currently there are only two possible startup functions, so we have them
    both here inside if (...) branches. In future we could switch to function
    pointers.
Sergey Petrunya's avatar
Sergey Petrunya committed
4405 4406

  TODO: consider moving this together with JOIN_TAB::preread_init
4407 4408
  
  RETURN 
psergey's avatar
psergey committed
4409 4410
    NESTED_LOOP_OK - OK
    NESTED_LOOP_ERROR| NESTED_LOOP_KILLED - Error, abort the join execution
4411 4412
*/

psergey's avatar
psergey committed
4413
enum_nested_loop_state join_tab_execution_startup(JOIN_TAB *tab)
4414 4415
{
  Item_in_subselect *in_subs;
4416
  DBUG_ENTER("join_tab_execution_startup");
Sergey Petrunya's avatar
Sergey Petrunya committed
4417
  
4418 4419 4420
  if (tab->table->pos_in_table_list && 
      (in_subs= tab->table->pos_in_table_list->jtbm_subselect))
  {
psergey's avatar
psergey committed
4421
    /* It's a non-merged SJM nest */
4422 4423 4424 4425 4426 4427 4428 4429 4430 4431
    DBUG_ASSERT(in_subs->engine->engine_type() ==
                subselect_engine::HASH_SJ_ENGINE);
    subselect_hash_sj_engine *hash_sj_engine=
      ((subselect_hash_sj_engine*)in_subs->engine);
    if (!hash_sj_engine->is_materialized)
    {
      hash_sj_engine->materialize_join->exec();
      hash_sj_engine->is_materialized= TRUE; 

      if (hash_sj_engine->materialize_join->error || tab->join->thd->is_fatal_error)
psergey's avatar
psergey committed
4432
        DBUG_RETURN(NESTED_LOOP_ERROR);
4433 4434
    }
  }
4435 4436 4437
  else if (tab->bush_children)
  {
    /* It's a merged SJM nest */
psergey's avatar
psergey committed
4438
    enum_nested_loop_state rc;
4439 4440 4441 4442
    SJ_MATERIALIZATION_INFO *sjm= tab->bush_children->start->emb_sj_nest->sj_mat_info;

    if (!sjm->materialized)
    {
4443 4444 4445
      JOIN *join= tab->join;
      JOIN_TAB *join_tab= tab->bush_children->start;
      JOIN_TAB *save_return_tab= join->return_tab;
4446 4447 4448 4449 4450 4451 4452 4453
      /*
        Now run the join for the inner tables. The first call is to run the
        join, the second one is to signal EOF (this is essential for some
        join strategies, e.g. it will make join buffering flush the records)
      */
      if ((rc= sub_select(join, join_tab, FALSE/* no EOF */)) < 0 ||
          (rc= sub_select(join, join_tab, TRUE/* now EOF */)) < 0)
      {
4454
        join->return_tab= save_return_tab;
4455 4456
        DBUG_RETURN(rc); /* it's NESTED_LOOP_(ERROR|KILLED)*/
      }
4457
      join->return_tab= save_return_tab;
4458 4459 4460 4461
      sjm->materialized= TRUE;
    }
  }

psergey's avatar
psergey committed
4462
  DBUG_RETURN(NESTED_LOOP_OK);
4463
}
4464

Sergey Petrunya's avatar
Sergey Petrunya committed
4465

4466 4467 4468 4469 4470 4471 4472 4473 4474 4475 4476 4477 4478 4479 4480 4481 4482 4483 4484 4485 4486 4487 4488 4489 4490 4491 4492 4493 4494 4495 4496 4497 4498 4499 4500 4501
/**
  Choose an optimal strategy to execute an IN/ALL/ANY subquery predicate
  based on cost.

  @param join_tables  the set of tables joined in the subquery

  @notes
  The method chooses between the materialization and IN=>EXISTS rewrite
  strategies for the execution of a non-flattened subquery IN predicate.
  The cost-based decision is made as follows:

  1. compute materialize_strategy_cost based on the unmodified subquery
  2. reoptimize the subquery taking into account the IN-EXISTS predicates
  3. compute in_exists_strategy_cost based on the reoptimized plan
  4. compare and set the cheaper strategy
     if (materialize_strategy_cost >= in_exists_strategy_cost)
       in_strategy = MATERIALIZATION
     else
       in_strategy = IN_TO_EXISTS
  5. if in_strategy = MATERIALIZATION and it is not possible to initialize it
       revert to IN_TO_EXISTS
  6. if (in_strategy == MATERIALIZATION)
       revert the subquery plan to the original one before reoptimizing
     else
       inject the IN=>EXISTS predicates into the new EXISTS subquery plan

  The implementation itself is a bit more complicated because it takes into
  account two more factors:
  - whether the user allowed both strategies through an optimizer_switch, and
  - if materialization was the cheaper strategy, whether it can be executed
    or not.

  @retval FALSE     success.
  @retval TRUE      error occurred.
*/

4502
bool JOIN::choose_subquery_plan(table_map join_tables)
unknown's avatar
unknown committed
4503
{
4504
  Join_plan_state save_qep; /* The original QEP of the subquery. */
4505
  enum_reopt_result reopt_result= REOPT_NONE;
4506 4507
  Item_in_subselect *in_subs;

4508 4509 4510 4511 4512 4513 4514
  /*
    IN/ALL/ANY optimizations are not applicable for so called fake select
    (this select exists only to filter results of union if it is needed).
  */
  if (select_lex == select_lex->master_unit()->fake_select_lex)
    return 0;

4515
  if (is_in_subquery())
4516
  {
4517
    in_subs= (Item_in_subselect*) unit->item;
4518 4519 4520 4521 4522
    if (in_subs->create_in_to_exists_cond(this))
      return true;
  }
  else
    return false;
unknown's avatar
unknown committed
4523 4524
  /* A strategy must be chosen earlier. */
  DBUG_ASSERT(in_subs->has_strategy());
4525 4526 4527
  DBUG_ASSERT(in_to_exists_where || in_to_exists_having);
  DBUG_ASSERT(!in_to_exists_where || in_to_exists_where->fixed);
  DBUG_ASSERT(!in_to_exists_having || in_to_exists_having->fixed);
4528

4529
  /*
4530 4531 4532
    Compute and compare the costs of materialization and in-exists if both
    strategies are possible and allowed by the user (checked during the prepare
    phase.
4533
  */
unknown's avatar
unknown committed
4534 4535
  if (in_subs->test_strategy(SUBS_MATERIALIZATION) &&
      in_subs->test_strategy(SUBS_IN_TO_EXISTS))
4536
  {
unknown's avatar
unknown committed
4537
    JOIN *outer_join;
4538
    JOIN *inner_join= this;
unknown's avatar
unknown committed
4539 4540 4541
    /* Number of unique value combinations filtered by the IN predicate. */
    double outer_lookup_keys;
    /* Cost and row count of the unmodified subquery. */
4542
    double inner_read_time_1, inner_record_count_1;
unknown's avatar
unknown committed
4543
    /* Cost of the subquery with injected IN-EXISTS predicates. */
unknown's avatar
unknown committed
4544
    double inner_read_time_2;
4545
    /* The cost to compute IN via materialization. */
4546
    double materialize_strategy_cost;
4547
    /* The cost of the IN->EXISTS strategy. */
4548
    double in_exists_strategy_cost;
unknown's avatar
unknown committed
4549
    double dummy;
4550

unknown's avatar
unknown committed
4551 4552 4553 4554 4555
    /*
      A. Estimate the number of rows of the outer table that will be filtered
      by the IN predicate.
    */
    outer_join= unit->outer_select() ? unit->outer_select()->join : NULL;
unknown's avatar
unknown committed
4556
    if (outer_join && outer_join->table_count > 0)
unknown's avatar
unknown committed
4557
    {
unknown's avatar
unknown committed
4558 4559 4560 4561 4562 4563 4564 4565 4566 4567 4568 4569
      /*
        TODO:
        Currently outer_lookup_keys is computed as the number of rows in
        the partial join including the JOIN_TAB where the IN predicate is
        pushed to. In the general case this is a gross overestimate because
        due to caching we are interested only in the number of unique keys.
        The search key may be formed by columns from much fewer than all
        tables in the partial join. Example:
        select * from t1, t2 where t1.c1 = t2.key AND t2.c2 IN (select ...);
        If the join order: t1, t2, the number of unique lookup keys is ~ to
        the number of unique values t2.c2 in the partial join t1 join t2.
      */
4570
      outer_join->get_partial_cost_and_fanout(in_subs->get_join_tab_idx(),
Sergey Petrunya's avatar
Sergey Petrunya committed
4571 4572
                                              table_map(-1),
                                              &dummy,
unknown's avatar
unknown committed
4573
                                              &outer_lookup_keys);
unknown's avatar
unknown committed
4574
    }
4575 4576
    else
    {
4577 4578 4579 4580
      /*
        TODO: outer_join can be NULL for DELETE statements.
        How to compute its cost?
      */
unknown's avatar
unknown committed
4581
      outer_lookup_keys= 1;
4582 4583
    }

unknown's avatar
unknown committed
4584 4585 4586 4587
    /*
      B. Estimate the cost and number of records of the subquery both
      unmodified, and with injected IN->EXISTS predicates.
    */
unknown's avatar
unknown committed
4588
    inner_read_time_1= inner_join->best_read;
unknown's avatar
unknown committed
4589
    inner_record_count_1= inner_join->record_count;
4590

Sergey Petrunya's avatar
Sergey Petrunya committed
4591
    if (in_to_exists_where && const_tables != table_count)
4592 4593
    {
      /*
4594 4595
        Re-optimize and cost the subquery taking into account the IN-EXISTS
        conditions.
4596
      */
unknown's avatar
unknown committed
4597 4598
      reopt_result= reoptimize(in_to_exists_where, join_tables, &save_qep);
      if (reopt_result == REOPT_ERROR)
4599 4600
        return TRUE;

unknown's avatar
unknown committed
4601
      /* Get the cost of the modified IN-EXISTS plan. */
unknown's avatar
unknown committed
4602 4603
      inner_read_time_2= inner_join->best_read;

4604 4605 4606 4607 4608
    }
    else
    {
      /* Reoptimization would not produce any better plan. */
      inner_read_time_2= inner_read_time_1;
4609
    }
4610 4611

    /*
unknown's avatar
unknown committed
4612
      C. Compute execution costs.
4613
    */
unknown's avatar
unknown committed
4614
    /* C.1 Compute the cost of the materialization strategy. */
4615 4616 4617
    //uint rowlen= get_tmp_table_rec_length(unit->first_select()->item_list);
    uint rowlen= get_tmp_table_rec_length(ref_pointer_array, 
                                          select_lex->item_list.elements);
unknown's avatar
unknown committed
4618 4619 4620
    /* The cost of writing one row into the temporary table. */
    double write_cost= get_tmp_table_write_cost(thd, inner_record_count_1,
                                                rowlen);
4621
    /* The cost of a lookup into the unique index of the materialized table. */
unknown's avatar
unknown committed
4622 4623
    double lookup_cost= get_tmp_table_lookup_cost(thd, inner_record_count_1,
                                                  rowlen);
4624
    /*
unknown's avatar
unknown committed
4625 4626
      The cost of executing the subquery and storing its result in an indexed
      temporary table.
4627
    */
unknown's avatar
unknown committed
4628 4629 4630
    double materialization_cost= inner_read_time_1 +
                                 write_cost * inner_record_count_1;

4631
    materialize_strategy_cost= materialization_cost +
unknown's avatar
unknown committed
4632
                               outer_lookup_keys * lookup_cost;
4633

unknown's avatar
unknown committed
4634 4635
    /* C.2 Compute the cost of the IN=>EXISTS strategy. */
    in_exists_strategy_cost= outer_lookup_keys * inner_read_time_2;
4636

unknown's avatar
unknown committed
4637
    /* C.3 Compare the costs and choose the cheaper strategy. */
4638
    if (materialize_strategy_cost >= in_exists_strategy_cost)
unknown's avatar
unknown committed
4639
      in_subs->set_strategy(SUBS_IN_TO_EXISTS);
4640
    else
unknown's avatar
unknown committed
4641
      in_subs->set_strategy(SUBS_MATERIALIZATION);
unknown's avatar
unknown committed
4642 4643 4644 4645 4646 4647 4648 4649

    DBUG_PRINT("info",
               ("mat_strategy_cost: %.2f, mat_cost: %.2f, write_cost: %.2f, lookup_cost: %.2f",
                materialize_strategy_cost, materialization_cost, write_cost, lookup_cost));
    DBUG_PRINT("info",
               ("inx_strategy_cost: %.2f, inner_read_time_2: %.2f",
                in_exists_strategy_cost, inner_read_time_2));
    DBUG_PRINT("info",("outer_lookup_keys: %.2f", outer_lookup_keys));
4650
  }
4651 4652

  /*
4653
    If (1) materialization is a possible strategy based on semantic analysis
4654 4655 4656 4657 4658
    during the prepare phase, then if
      (2) it is more expensive than the IN->EXISTS transformation, and
      (3) it is not possible to create usable indexes for the materialization
          strategy,
      fall back to IN->EXISTS.
4659 4660
    otherwise
      use materialization.
4661
  */
unknown's avatar
unknown committed
4662
  if (in_subs->test_strategy(SUBS_MATERIALIZATION) &&
4663
      in_subs->setup_mat_engine())
4664 4665
  {
    /*
4666 4667 4668
      If materialization was the cheaper or the only user-selected strategy,
      but it is not possible to execute it due to limitations in the
      implementation, fall back to IN-TO-EXISTS.
4669
    */
unknown's avatar
unknown committed
4670
    in_subs->set_strategy(SUBS_IN_TO_EXISTS);
4671
  }
4672

unknown's avatar
unknown committed
4673
  if (in_subs->test_strategy(SUBS_MATERIALIZATION))
4674
  {
4675 4676
    /* Restore the original query plan used for materialization. */
    if (reopt_result == REOPT_NEW_PLAN)
unknown's avatar
unknown committed
4677
      restore_query_plan(&save_qep);
4678

4679 4680
    in_subs->unit->uncacheable&= ~UNCACHEABLE_DEPENDENT_INJECTED;
    select_lex->uncacheable&= ~UNCACHEABLE_DEPENDENT_INJECTED;
4681

4682 4683 4684 4685 4686 4687 4688 4689 4690 4691 4692 4693 4694 4695 4696
    /*
      Reset the "LIMIT 1" set in Item_exists_subselect::fix_length_and_dec.
      TODO:
      Currently we set the subquery LIMIT to infinity, and this is correct
      because we forbid at parse time LIMIT inside IN subqueries (see
      Item_in_subselect::test_limit). However, once we allow this, here
      we should set the correct limit if given in the query.
    */
    in_subs->unit->global_parameters->select_limit= NULL;
    in_subs->unit->set_limit(unit->global_parameters);
    /*
      Set the limit of this JOIN object as well, because normally its being
      set in the beginning of JOIN::optimize, which was already done.
    */
    select_limit= in_subs->unit->select_limit_cnt;
4697
  }
unknown's avatar
unknown committed
4698
  else if (in_subs->test_strategy(SUBS_IN_TO_EXISTS))
4699
  {
unknown's avatar
unknown committed
4700
    if (reopt_result == REOPT_NONE && in_to_exists_where &&
Sergey Petrunya's avatar
Sergey Petrunya committed
4701
        const_tables != table_count)
4702
    {
4703
      /*
unknown's avatar
unknown committed
4704 4705 4706
        The subquery was not reoptimized with the newly injected IN-EXISTS
        conditions either because the user allowed only the IN-EXISTS strategy,
        or because materialization was not possible based on semantic analysis.
4707
      */
unknown's avatar
unknown committed
4708 4709
      reopt_result= reoptimize(in_to_exists_where, join_tables, NULL);
      if (reopt_result == REOPT_ERROR)
4710 4711 4712 4713 4714
        return TRUE;
    }

    if (in_subs->inject_in_to_exists_cond(this))
      return TRUE;
4715 4716 4717 4718
    /*
      It is IN->EXISTS transformation so we should mark subquery as
      dependent
    */
4719 4720 4721
    in_subs->unit->uncacheable|= UNCACHEABLE_DEPENDENT_INJECTED;
    select_lex->uncacheable|= UNCACHEABLE_DEPENDENT_INJECTED;
    select_limit= 1;
4722 4723 4724 4725
  }
  else
    DBUG_ASSERT(FALSE);

4726
  return FALSE;
4727
}
4728 4729 4730 4731 4732 4733 4734 4735 4736 4737 4738 4739 4740


/**
  Choose a query plan for a table-less subquery.

  @notes

  @retval FALSE     success.
  @retval TRUE      error occurred.
*/

bool JOIN::choose_tableless_subquery_plan()
{
Sergey Petrunya's avatar
Sergey Petrunya committed
4741
  DBUG_ASSERT(!tables_list || !table_count);
4742
  if (unit->item)
4743
  {
4744 4745
    DBUG_ASSERT(unit->item->type() == Item::SUBSELECT_ITEM);
    Item_subselect *subs_predicate= unit->item;
4746 4747 4748 4749 4750 4751 4752 4753 4754 4755 4756 4757 4758 4759 4760 4761 4762 4763 4764 4765 4766 4767 4768 4769 4770 4771 4772 4773 4774 4775 4776 4777 4778

    /*
      If the optimizer determined that his query has an empty result,
      in most cases the subquery predicate is a known constant value -
      either FALSE or NULL. The implementation of Item_subselect::reset()
      determines which one.
    */
    if (zero_result_cause)
    {
      if (!implicit_grouping)
      {
        /*
          Both group by queries and non-group by queries without aggregate
          functions produce empty subquery result.
        */
        subs_predicate->reset();
        subs_predicate->make_const();
        return FALSE;
      }

      /* TODO:
         A further optimization is possible when a non-group query with
         MIN/MAX/COUNT is optimized by opt_sum_query. Then, if there are
         only MIN/MAX functions over an empty result set, the subquery
         result is a NULL value/row, thus the value of subs_predicate is
         NULL.
      */
    }

    if (subs_predicate->is_in_predicate())
    {
      Item_in_subselect *in_subs;
      in_subs= (Item_in_subselect*) subs_predicate;
unknown's avatar
unknown committed
4779
      in_subs->set_strategy(SUBS_IN_TO_EXISTS);
4780 4781 4782 4783 4784 4785 4786 4787
      if (in_subs->create_in_to_exists_cond(this) ||
          in_subs->inject_in_to_exists_cond(this))
        return TRUE;
      tmp_having= having;
    }
  }
  return FALSE;
}