BUG#787299: Valgrind complains on a join query with two IN subqueries

- Don't attempt to construct FirstMatch access method if we've 
  just figured three lines above that it can't be used (because join
  prefix doesn't have the needed tables), and so have set 
    pos->first_firstmatch_table= MAX_TABLES 
  Attempts to analyze join->positions[MAX_TABLES] caused valgrind warnings

mysql-test/r/subselect_sj.result

@@ -1245,4 +1245,25 @@ t1field
 2
 3
 drop table t1,t2;
+# 
+# BUG#787299: Valgrind complains on a join query with two IN subqueries
+#
+create table t1 (a int);
+insert into t1 values (1), (2), (3);
+create table t2 as select * from t1;
+select * from t1 A, t1 B
+where A.a = B.a and A.a in (select a from t2 C) and B.a in (select a from t2 D);
+a	a
+1	1
+2	2
+3	3
+explain
+select * from t1 A, t1 B
+where A.a = B.a and A.a in (select a from t2 C) and B.a in (select a from t2 D);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	A	ALL	NULL	NULL	NULL	NULL	3	Start temporary
+1	PRIMARY	B	ALL	NULL	NULL	NULL	NULL	3	Using where; Using join buffer (flat, BNL join)
+1	PRIMARY	C	ALL	NULL	NULL	NULL	NULL	3	Using where; Using join buffer (flat, BNL join)
+1	PRIMARY	D	ALL	NULL	NULL	NULL	NULL	3	Using where; End temporary; Using join buffer (flat, BNL join)
+drop table t1, t2;
 set @@optimizer_switch=@save_optimizer_switch;

mysql-test/r/subselect_sj_jcl6.result

@@ -1253,6 +1253,27 @@ t1field
 2
 3
 drop table t1,t2;
+# 
+# BUG#787299: Valgrind complains on a join query with two IN subqueries
+#
+create table t1 (a int);
+insert into t1 values (1), (2), (3);
+create table t2 as select * from t1;
+select * from t1 A, t1 B
+where A.a = B.a and A.a in (select a from t2 C) and B.a in (select a from t2 D);
+a	a
+1	1
+2	2
+3	3
+explain
+select * from t1 A, t1 B
+where A.a = B.a and A.a in (select a from t2 C) and B.a in (select a from t2 D);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	A	ALL	NULL	NULL	NULL	NULL	3	Start temporary
+1	PRIMARY	B	ALL	NULL	NULL	NULL	NULL	3	Using where; Using join buffer (flat, BNL join)
+1	PRIMARY	C	ALL	NULL	NULL	NULL	NULL	3	Using where; Using join buffer (incremental, BNL join)
+1	PRIMARY	D	ALL	NULL	NULL	NULL	NULL	3	Using where; End temporary; Using join buffer (incremental, BNL join)
+drop table t1, t2;
 set @@optimizer_switch=@save_optimizer_switch;
 #
 # BUG#49129: Wrong result with IN-subquery with join_cache_level=6 and firstmatch=off

mysql-test/t/subselect_sj.test

@@ -1137,5 +1137,18 @@ WHERE
                 WHERE C.t2field IN (SELECT D.t2field FROM t2 D));
 drop table t1,t2;
 
+--echo # 
+--echo # BUG#787299: Valgrind complains on a join query with two IN subqueries
+--echo #
+create table t1 (a int);
+insert into t1 values (1), (2), (3);
+create table t2 as select * from t1;
+select * from t1 A, t1 B
+ where A.a = B.a and A.a in (select a from t2 C) and B.a in (select a from t2 D);
+explain
+select * from t1 A, t1 B
+ where A.a = B.a and A.a in (select a from t2 C) and B.a in (select a from t2 D);
+drop table t1, t2;
+
 # The following command must be the last one the file 
 set @@optimizer_switch=@save_optimizer_switch;

sql/opt_subselect.cc

@@ -2042,7 +2042,7 @@ void advance_sj_state(JOIN *join, table_map remaining_tables,
   /* Initialize the state or copy it from prev. tables */
   if (idx == join->const_tables)
   {
-    pos->first_firstmatch_table= MAX_TABLES;
+    pos->invalidate_firstmatch_prefix();
     pos->first_loosescan_table= MAX_TABLES; 
     pos->dupsweedout_tables= 0;
     pos->sjm_scan_need_tables= 0;
@@ -2107,7 +2107,7 @@ void advance_sj_state(JOIN *join, table_map remaining_tables,
       pos->first_firstmatch_rtbl= remaining_tables;
     }
 
-    if (pos->first_firstmatch_table != MAX_TABLES)
+    if (pos->in_firstmatch_prefix())
     {
       if (outer_corr_tables & pos->first_firstmatch_rtbl)
       {
@@ -2115,7 +2115,7 @@ void advance_sj_state(JOIN *join, table_map remaining_tables,
           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.
         */
-        pos->first_firstmatch_table= MAX_TABLES;
+        pos->invalidate_firstmatch_prefix();
       }
       else
       {
@@ -2123,7 +2123,8 @@ void advance_sj_state(JOIN *join, table_map remaining_tables,
         pos->firstmatch_need_tables|= sj_inner_tables;
       }
     
-      if (!(pos->firstmatch_need_tables & remaining_tables))
+      if (pos->in_firstmatch_prefix() && 
+          !(pos->firstmatch_need_tables & remaining_tables))
       {
         /*
           Got a complete FirstMatch range.

sql/sql_select.h

@@ -584,6 +584,8 @@ typedef struct st_position
    */
   table_map firstmatch_need_tables;
 
+  bool in_firstmatch_prefix() { return (first_firstmatch_table != MAX_TABLES); }
+  void invalidate_firstmatch_prefix() { first_firstmatch_table= MAX_TABLES; }
 
 /* Duplicate Weedout strategy */
   /* The first table that the strategy will need to handle */