Semi-join optimizations code cleanup:

- Break down POSITION/advance_sj_state() into four classes 
  representing potential semi-join strategies.

- Treat all strategies uniformly (before, DuplicateWeedout 
  was special as it was the catch-all strategy. Now, we're 
  still relying on it to be the catch-all, but are able to 
  function,e.g. with firstmatch=on,duplicate_weedout=off.

- Update test results (checked)

mysql-test/r/subselect_sj2.result

@@ -323,8 +323,8 @@ WHERE Language='English' AND Percentage > 10 AND
 t2.Population > 100000);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	range	Population,Country	Population	4	NULL	1	Using index condition; Rowid-ordered scan; Start temporary
-1	PRIMARY	t2	eq_ref	PRIMARY,Population	PRIMARY	3	test.t1.Country	1	Using where
-1	PRIMARY	t3	eq_ref	PRIMARY,Percentage	PRIMARY	33	test.t1.Country,const	1	Using index condition; Using where; End temporary
+1	PRIMARY	t2	eq_ref	PRIMARY,Population	PRIMARY	3	test.t1.Country	1	Using where; End temporary
+1	PRIMARY	t3	eq_ref	PRIMARY,Percentage	PRIMARY	33	test.t1.Country,const	1	Using index condition; Using where
 set optimizer_switch=@bug35674_save_optimizer_switch;
 DROP TABLE t1,t2,t3;
 CREATE TABLE t1 (

mysql-test/r/subselect_sj2_jcl6.result

@@ -332,8 +332,8 @@ WHERE Language='English' AND Percentage > 10 AND
 t2.Population > 100000);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	range	Population,Country	Population	4	NULL	1	Using index condition; Rowid-ordered scan; Start temporary
-1	PRIMARY	t2	eq_ref	PRIMARY,Population	PRIMARY	3	test.t1.Country	1	Using where; Using join buffer (flat, BKA join); Key-ordered Rowid-ordered scan
-1	PRIMARY	t3	eq_ref	PRIMARY,Percentage	PRIMARY	33	test.t1.Country,const	1	Using index condition; Using where; End temporary; Using join buffer (incremental, BKA join); Key-ordered Rowid-ordered scan
+1	PRIMARY	t2	eq_ref	PRIMARY,Population	PRIMARY	3	test.t1.Country	1	Using where; End temporary; Using join buffer (flat, BKA join); Key-ordered Rowid-ordered scan
+1	PRIMARY	t3	eq_ref	PRIMARY,Percentage	PRIMARY	33	test.t1.Country,const	1	Using index condition; Using where; Using join buffer (incremental, BKA join); Key-ordered Rowid-ordered scan
 set optimizer_switch=@bug35674_save_optimizer_switch;
 DROP TABLE t1,t2,t3;
 CREATE TABLE t1 (

sql/opt_subselect.h

@@ -263,8 +263,8 @@ class Loose_scan_opt
     {
       pos->records_read=    best_loose_scan_records;
       pos->key=             best_loose_scan_start_key;
-      pos->loosescan_key=   best_loose_scan_key;
-      pos->loosescan_parts= best_max_loose_keypart + 1;
+      pos->loosescan_picker.loosescan_key=   best_loose_scan_key;
+      pos->loosescan_picker.loosescan_parts= best_max_loose_keypart + 1;
       pos->use_join_buffer= FALSE;
       pos->table=           tab;
       // todo need ref_depend_map ?
@@ -277,8 +277,7 @@ class Loose_scan_opt
 };
 
 
-void advance_sj_state(JOIN *join, const table_map remaining_tables, 
-                      const JOIN_TAB *new_join_tab, uint idx, 
+void advance_sj_state(JOIN *join, const table_map remaining_tables, uint idx, 
                       double *current_record_count, double *current_read_time,
                       POSITION *loose_scan_pos);
 void restore_prev_sj_state(const table_map remaining_tables, 

sql/sql_select.cc

@@ -85,7 +85,7 @@ static int join_tab_cmp_embedded_first(const void *emb, const void* ptr1, const
 static bool find_best(JOIN *join,table_map rest_tables,uint index,
 		      double record_count,double read_time);
 static uint cache_record_length(JOIN *join,uint index);
-static bool get_best_combination(JOIN *join);
+bool get_best_combination(JOIN *join);
 static store_key *get_store_key(THD *thd,
 				KEYUSE *keyuse, table_map used_tables,
 				KEY_PART_INFO *key_part, uchar *key_buff,
@@ -4883,7 +4883,7 @@ void set_position(JOIN *join,uint idx,JOIN_TAB *table,KEYUSE *key)
   join->positions[idx].records_read=1.0;	/* This is a const table */
   join->positions[idx].ref_depend_map= 0;
 
-  join->positions[idx].loosescan_key= MAX_KEY; /* Not a LooseScan */
+//  join->positions[idx].loosescan_key= MAX_KEY; /* Not a LooseScan */
   join->positions[idx].sj_strategy= SJ_OPT_NONE;
   join->positions[idx].use_join_buffer= FALSE;
 
@@ -5533,7 +5533,7 @@ best_access_path(JOIN      *join,
   pos->key=          best_key;
   pos->table=        s;
   pos->ref_depend_map= best_ref_depends_map;
-  pos->loosescan_key= MAX_KEY;
+  pos->loosescan_picker.loosescan_key= MAX_KEY;
   pos->use_join_buffer= best_uses_jbuf;
    
   loose_scan_opt.save_to_position(s, loose_scan_pos);
@@ -5840,7 +5840,7 @@ optimize_straight_join(JOIN *join, table_map join_tables)
     /* compute the cost of the new plan extended with 's' */
     record_count*= join->positions[idx].records_read;
     read_time+=    join->positions[idx].read_time;
-    advance_sj_state(join, join_tables, s, idx, &record_count, &read_time,
+    advance_sj_state(join, join_tables, idx, &record_count, &read_time,
                      &loose_scan_pos);
 
     join_tables&= ~(s->table->map);
@@ -6356,7 +6356,7 @@ best_extension_by_limited_search(JOIN      *join,
       current_record_count= record_count * position->records_read;
       current_read_time=    read_time + position->read_time;
 
-      advance_sj_state(join, remaining_tables, s, idx, &current_record_count,
+      advance_sj_state(join, remaining_tables, idx, &current_record_count,
                        &current_read_time, &loose_scan_pos);
 
       /* Expand only partial plans with lower cost than the best QEP so far */
@@ -6513,7 +6513,7 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
       */
       double current_record_count=record_count*records;
       double current_read_time=read_time+best;
-      advance_sj_state(join, rest_tables, s, idx, &current_record_count, 
+      advance_sj_state(join, rest_tables, idx, &current_record_count, 
                        &current_read_time, &loose_scan_pos);
 
       if (best_record_count > current_record_count ||
@@ -7013,7 +7013,7 @@ static Item * const null_ptr= NULL;
     TRUE   Out of memory
 */
 
-static bool
+bool
 get_best_combination(JOIN *join)
 {
   uint tablenr;
@@ -7091,13 +7091,6 @@ get_best_combination(JOIN *join)
     
     *j= *join->best_positions[tablenr].table;
 
-#if 0
-/* SJ-Materialization is represented with join tab ranges */
-    if (j->sj_strategy == SJ_OPT_MATERIALIZE || 
-        j->sj_strategy == SJ_OPT_MATERIALIZE)
-      j->sj_strategy= SJ_OPT_NONE;  
-#endif
-
     j->bush_root_tab= sjm_nest_root;
 
     form=join->table[tablenr]=j->table;
@@ -7120,7 +7113,7 @@ get_best_combination(JOIN *join)
         (join->best_positions[tablenr].sj_strategy == SJ_OPT_LOOSE_SCAN))
     {
       j->type=JT_ALL;
-      j->index= join->best_positions[tablenr].loosescan_key;
+      j->index= join->best_positions[tablenr].loosescan_picker.loosescan_key;
       if (tablenr != join->const_tables)
 	join->full_join=1;
     }