Fix bug mdev-447: Wrong output from the EXPLAIN command of the test case for lp bug #714999

The fix backports from MWL#182: Explain running statements the logic that
saves the original JOIN_TAB array of a query plan after optimization. This
array is later used during EXPLAIN to iterate over the original JOIN plan
nodes in the cases when this plan could be changed by early subquery
execution during the optimization phase of the outer query.

mysql-test/r/subselect.result

@@ -4196,7 +4196,7 @@ INSERT INTO t1 VALUES (1,1),(2,1);
 EXPLAIN SELECT 1 FROM t1 WHERE a = (SELECT COUNT(*) FROM t1 GROUP BY b);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ref	a	a	5	const	1	Using where; Using index
-2	SUBQUERY	internal_tmp_table	ALL	group_key	NULL	NULL	NULL	1	Using temporary; Using filesort
+2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using temporary; Using filesort
 DROP TABLE t1;
 CREATE TABLE t1 (id int NOT NULL, st CHAR(2), INDEX idx(id));
 INSERT INTO t1 VALUES

mysql-test/r/subselect_innodb.result

@@ -333,7 +333,7 @@ WHERE (SELECT DISTINCT b FROM t3) > 0);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	const	PRIMARY	PRIMARY	4	const	1	Using where; Using index
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
-3	SUBQUERY	internal_tmp_table	ALL	group_key	NULL	NULL	NULL	0	Using temporary
+3	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	1	Using temporary
 SELECT *
 FROM t1
 WHERE t1.a = (
@@ -386,7 +386,7 @@ select 1 from t1 where 1 like (select 1 from t1 where 1 <=> (select 1 from t1 gr
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	1	
 2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	1	
-3	SUBQUERY	internal_tmp_table	ALL	group_key	NULL	NULL	NULL	1	Using temporary; Using filesort
+3	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	1	Using temporary; Using filesort
 select 1 from t1 where 1 like (select 1 from t1 where 1 <=> (select 1 from t1 group by a1));
 1
 1

mysql-test/r/subselect_mat_cost_bugs.result

@@ -148,7 +148,7 @@ FROM t2 GROUP BY f1
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 2	SUBQUERY	t1	system	NULL	NULL	NULL	NULL	1	
-3	SUBQUERY	internal_tmp_table	ALL	group_key	NULL	NULL	NULL	1	Using temporary; Using filesort
+3	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	Using temporary; Using filesort
 drop table t1, t2, t3;
 #
 # LP BUG#715034 Item_sum_distinct::clear(): Assertion `tree != 0' failed

mysql-test/r/subselect_no_mat.result

@@ -4200,7 +4200,7 @@ INSERT INTO t1 VALUES (1,1),(2,1);
 EXPLAIN SELECT 1 FROM t1 WHERE a = (SELECT COUNT(*) FROM t1 GROUP BY b);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ref	a	a	5	const	1	Using where; Using index
-2	SUBQUERY	internal_tmp_table	ALL	group_key	NULL	NULL	NULL	1	Using temporary; Using filesort
+2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using temporary; Using filesort
 DROP TABLE t1;
 CREATE TABLE t1 (id int NOT NULL, st CHAR(2), INDEX idx(id));
 INSERT INTO t1 VALUES

mysql-test/r/subselect_no_opts.result

@@ -4196,7 +4196,7 @@ INSERT INTO t1 VALUES (1,1),(2,1);
 EXPLAIN SELECT 1 FROM t1 WHERE a = (SELECT COUNT(*) FROM t1 GROUP BY b);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ref	a	a	5	const	1	Using where; Using index
-2	SUBQUERY	internal_tmp_table	ALL	group_key	NULL	NULL	NULL	1	Using temporary; Using filesort
+2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using temporary; Using filesort
 DROP TABLE t1;
 CREATE TABLE t1 (id int NOT NULL, st CHAR(2), INDEX idx(id));
 INSERT INTO t1 VALUES

mysql-test/r/subselect_no_scache.result

@@ -4202,7 +4202,7 @@ INSERT INTO t1 VALUES (1,1),(2,1);
 EXPLAIN SELECT 1 FROM t1 WHERE a = (SELECT COUNT(*) FROM t1 GROUP BY b);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ref	a	a	5	const	1	Using where; Using index
-2	SUBQUERY	internal_tmp_table	ALL	group_key	NULL	NULL	NULL	1	Using temporary; Using filesort
+2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using temporary; Using filesort
 DROP TABLE t1;
 CREATE TABLE t1 (id int NOT NULL, st CHAR(2), INDEX idx(id));
 INSERT INTO t1 VALUES

mysql-test/r/subselect_no_semijoin.result

@@ -4196,7 +4196,7 @@ INSERT INTO t1 VALUES (1,1),(2,1);
 EXPLAIN SELECT 1 FROM t1 WHERE a = (SELECT COUNT(*) FROM t1 GROUP BY b);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ref	a	a	5	const	1	Using where; Using index
-2	SUBQUERY	internal_tmp_table	ALL	group_key	NULL	NULL	NULL	1	Using temporary; Using filesort
+2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using temporary; Using filesort
 DROP TABLE t1;
 CREATE TABLE t1 (id int NOT NULL, st CHAR(2), INDEX idx(id));
 INSERT INTO t1 VALUES

sql/sql_select.cc

@@ -271,8 +271,11 @@ Item_equal *find_item_equal(COND_EQUAL *cond_equal, Field *field,
                             bool *inherited_fl);
 JOIN_TAB *first_depth_first_tab(JOIN* join);
 JOIN_TAB *next_depth_first_tab(JOIN* join, JOIN_TAB* tab);
-JOIN_TAB *first_breadth_first_tab(JOIN *join);
-JOIN_TAB *next_breadth_first_tab(JOIN *join, JOIN_TAB *tab);
+
+enum enum_exec_or_opt {WALK_OPTIMIZATION_TABS , WALK_EXECUTION_TABS};
+JOIN_TAB *first_breadth_first_tab(JOIN *join, enum enum_exec_or_opt tabs_kind);
+JOIN_TAB *next_breadth_first_tab(JOIN *join, enum enum_exec_or_opt tabs_kind,
+                                 JOIN_TAB *tab);
 
 /**
   This handles SELECT with and without UNION.
@@ -6649,12 +6652,12 @@ double JOIN::get_examined_rows()
 {
   ha_rows examined_rows;
   double prev_fanout= 1;
-  JOIN_TAB *tab= first_breadth_first_tab(this);
+  JOIN_TAB *tab= first_breadth_first_tab(this, WALK_OPTIMIZATION_TABS);
   JOIN_TAB *prev_tab= tab;
 
   examined_rows= tab->get_examined_rows();
 
-  while ((tab= next_breadth_first_tab(this, tab)))
+  while ((tab= next_breadth_first_tab(this, WALK_OPTIMIZATION_TABS, tab)))
   {
     prev_fanout *= prev_tab->records_read;
     examined_rows+= (ha_rows) (tab->get_examined_rows() * prev_fanout);
@@ -7269,23 +7272,30 @@ prev_record_reads(POSITION *positions, uint idx, table_map found_ref)
   Enumerate join tabs in breadth-first fashion, including const tables.
 */
 
-JOIN_TAB *first_breadth_first_tab(JOIN *join)
+JOIN_TAB *first_breadth_first_tab(JOIN *join, enum enum_exec_or_opt tabs_kind)
 {
-  return join->join_tab; /* There's always one (i.e. first) table */
+  /* There's always one (i.e. first) table */
+  return (tabs_kind == WALK_EXECUTION_TABS)? join->join_tab:
+                                             join->table_access_tabs;
 }
 
 
-JOIN_TAB *next_breadth_first_tab(JOIN *join, JOIN_TAB *tab)
+JOIN_TAB *next_breadth_first_tab(JOIN *join, enum enum_exec_or_opt tabs_kind,
+                                 JOIN_TAB *tab)
 {
+  JOIN_TAB* const first_top_tab= first_breadth_first_tab(join, tabs_kind);
+  const uint n_top_tabs_count= (tabs_kind == WALK_EXECUTION_TABS)? 
+                                  join->top_join_tab_count:
+                                  join->top_table_access_tabs_count;
   if (!tab->bush_root_tab)
   {
     /* We're at top level. Get the next top-level tab */
     tab++;
-    if (tab < join->join_tab + join->top_join_tab_count)
+    if (tab < first_top_tab + n_top_tabs_count)
       return tab;
 
     /* No more top-level tabs. Switch to enumerating SJM nest children */
-    tab= join->join_tab;
+    tab= first_top_tab;
   }
   else
   {
@@ -7309,7 +7319,7 @@ JOIN_TAB *next_breadth_first_tab(JOIN *join, JOIN_TAB *tab)
     Ok, "tab" points to a top-level table, and we need to find the next SJM
     nest and enter it.
   */
-  for (; tab < join->join_tab + join->top_join_tab_count; tab++)
+  for (; tab < first_top_tab + n_top_tabs_count; tab++)
   {
     if (tab->bush_children)
       return tab->bush_children->start;
@@ -7333,7 +7343,7 @@ JOIN_TAB *first_top_level_tab(JOIN *join, enum enum_with_const_tables with_const
 
 JOIN_TAB *next_top_level_tab(JOIN *join, JOIN_TAB *tab)
 {
-  tab= next_breadth_first_tab(join, tab);
+  tab= next_breadth_first_tab(join, WALK_EXECUTION_TABS, tab);
   if (tab && tab->bush_root_tab)
     tab= NULL;
   return tab;
@@ -7633,6 +7643,12 @@ get_best_combination(JOIN *join)
 
   join->top_join_tab_count= join->join_tab_ranges.head()->end - 
                             join->join_tab_ranges.head()->start;
+  /*
+    Save pointers to select join tabs for SHOW EXPLAIN
+  */
+  join->table_access_tabs= join->join_tab;
+  join->top_table_access_tabs_count= join->top_join_tab_count;
+
   update_depend_map(join);
   DBUG_RETURN(0);
 }
@@ -21389,8 +21405,8 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
     bool printing_materialize_nest= FALSE;
     uint select_id= join->select_lex->select_number;
 
-    for (JOIN_TAB *tab= first_breadth_first_tab(join); tab;
-         tab= next_breadth_first_tab(join, tab))
+    for (JOIN_TAB *tab= first_breadth_first_tab(join, WALK_OPTIMIZATION_TABS); tab;
+         tab= next_breadth_first_tab(join, WALK_OPTIMIZATION_TABS, tab))
     {
       if (tab->bush_root_tab)
       {
@@ -21473,16 +21489,8 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
       else
       {
         TABLE_LIST *real_table= table->pos_in_table_list;
-        /*
-          Internal temporary tables have no corresponding table reference
-          object. Such a table may appear in EXPLAIN when a subquery that needs
-          a temporary table has been executed, and JOIN::exec replaced the
-          original JOIN with a plan to access the data in the temp table
-          (made by JOIN::make_simple_join).
-        */
-        const char *tab_name= real_table ? real_table->alias :
-                                           "internal_tmp_table";
-	item_list.push_back(new Item_string(tab_name, strlen(tab_name), cs));
+	item_list.push_back(new Item_string(real_table->alias,
+                                            strlen(real_table->alias), cs));
       }
       /* "partitions" column */
       if (join->thd->lex->describe & DESCRIBE_PARTITIONS)

sql/sql_select.h

@@ -897,6 +897,19 @@ class JOIN :public Sql_alloc
 
 public:
   JOIN_TAB *join_tab, **best_ref;
+
+  /*
+    For "Using temporary+Using filesort" queries, JOIN::join_tab can point to
+    either: 
+    1. array of join tabs describing how to run the select, or
+    2. array of single join tab describing read from the temporary table.
+
+    SHOW EXPLAIN code needs to read/show #1. This is why two next members are
+    there for saving it.
+  */
+  JOIN_TAB *table_access_tabs;
+  uint     top_table_access_tabs_count;
+
   JOIN_TAB **map2table;    ///< mapping between table indexes and JOIN_TABs
   JOIN_TAB *join_tab_save; ///< saved join_tab for subquery reexecution