Fixed LP bug #887496.

This bug in the function Loose_scan_opt::check_ref_access_part1 could lead
to choosing an invalid execution plan employing a loose scan access to a
semi-join table even in the cases when such access could not be used at all.
This could result in wrong answers for some queries with IN subqueries.

mysql-test/r/subselect_mat_cost_bugs.result

@@ -346,8 +346,8 @@ WHERE t4.a >= t3.b
 AND a = SOME (SELECT b FROM t5));
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t3	ALL	NULL	NULL	NULL	NULL	2	Using where
-2	DEPENDENT SUBQUERY	t5	index	c	c	10	NULL	2	Using where; Using index; LooseScan
-2	DEPENDENT SUBQUERY	t4	eq_ref	PRIMARY	PRIMARY	4	test.t5.b	1	Using index condition; Using where
+2	DEPENDENT SUBQUERY	t5	index	c	c	10	NULL	2	Using where; Using index; Start temporary
+2	DEPENDENT SUBQUERY	t4	eq_ref	PRIMARY	PRIMARY	4	test.t5.b	1	Using index condition; Using where; End temporary
 SELECT *
 FROM t3
 WHERE t3.b > ALL (

mysql-test/r/subselect_sj.result

@@ -2050,4 +2050,37 @@ a
 3
 set optimizer_switch= @tmp_otimizer_switch;
 drop table t1,t2;
+#
+# Bug #887496: semijoin with IN equality for the second part of an index
+#
+CREATE TABLE t1 (a int);
+INSERT INTO t1 VALUES (9), (0), (8), (5);
+CREATE TABLE t2 (a int, b varchar(1), INDEX idx (b,a));
+INSERT INTO t2 VALUES (5,'r'), (5,'z');
+CREATE TABLE t3 (a int, b varchar(1), INDEX idx (b,a));
+INSERT INTO t3 VALUES (5,'r'), (5,'z');
+set @tmp_otimizer_switch= @@optimizer_switch;
+SET SESSION optimizer_switch='semijoin=on,firstmatch=on';
+SET SESSION optimizer_switch='loosescan=off';
+EXPLAIN
+SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t2	index	idx	idx	9	NULL	2	Using where; Using index; Start temporary
+1	PRIMARY	t3	ref	idx	idx	4	test.t2.b	1	Using index
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	Using where; End temporary; Using join buffer (flat, BNL join)
+SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
+a
+5
+SET SESSION optimizer_switch='loosescan=on';
+EXPLAIN
+SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t2	index	idx	idx	9	NULL	2	Using where; Using index; Start temporary
+1	PRIMARY	t3	ref	idx	idx	4	test.t2.b	1	Using index
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	Using where; End temporary; Using join buffer (flat, BNL join)
+SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
+a
+5
+set optimizer_switch= @tmp_otimizer_switch;
+DROP TABLE t1,t2,t3;
 set optimizer_switch=@subselect_sj_tmp;

mysql-test/r/subselect_sj_jcl6.result

@@ -2061,6 +2061,39 @@ a
 3
 set optimizer_switch= @tmp_otimizer_switch;
 drop table t1,t2;
+#
+# Bug #887496: semijoin with IN equality for the second part of an index
+#
+CREATE TABLE t1 (a int);
+INSERT INTO t1 VALUES (9), (0), (8), (5);
+CREATE TABLE t2 (a int, b varchar(1), INDEX idx (b,a));
+INSERT INTO t2 VALUES (5,'r'), (5,'z');
+CREATE TABLE t3 (a int, b varchar(1), INDEX idx (b,a));
+INSERT INTO t3 VALUES (5,'r'), (5,'z');
+set @tmp_otimizer_switch= @@optimizer_switch;
+SET SESSION optimizer_switch='semijoin=on,firstmatch=on';
+SET SESSION optimizer_switch='loosescan=off';
+EXPLAIN
+SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t2	index	idx	idx	9	NULL	2	Using where; Using index; Start temporary
+1	PRIMARY	t3	ref	idx	idx	4	test.t2.b	1	Using index
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	Using where; End temporary; Using join buffer (flat, BNL join)
+SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
+a
+5
+SET SESSION optimizer_switch='loosescan=on';
+EXPLAIN
+SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t2	index	idx	idx	9	NULL	2	Using where; Using index; Start temporary
+1	PRIMARY	t3	ref	idx	idx	4	test.t2.b	1	Using index
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	Using where; End temporary; Using join buffer (flat, BNL join)
+SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
+a
+5
+set optimizer_switch= @tmp_otimizer_switch;
+DROP TABLE t1,t2,t3;
 set optimizer_switch=@subselect_sj_tmp;
 #
 # BUG#49129: Wrong result with IN-subquery with join_cache_level=6 and firstmatch=off

mysql-test/t/subselect_sj.test

@@ -1880,5 +1880,35 @@ set optimizer_switch= @tmp_otimizer_switch;
 
 drop table t1,t2;
 
+--echo #
+--echo # Bug #887496: semijoin with IN equality for the second part of an index
+--echo #
+
+CREATE TABLE t1 (a int);
+INSERT INTO t1 VALUES (9), (0), (8), (5);
+
+CREATE TABLE t2 (a int, b varchar(1), INDEX idx (b,a));
+INSERT INTO t2 VALUES (5,'r'), (5,'z');
+
+CREATE TABLE t3 (a int, b varchar(1), INDEX idx (b,a));
+INSERT INTO t3 VALUES (5,'r'), (5,'z');
+
+set @tmp_otimizer_switch= @@optimizer_switch;
+SET SESSION optimizer_switch='semijoin=on,firstmatch=on';
+
+SET SESSION optimizer_switch='loosescan=off';
+EXPLAIN
+SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
+SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
+
+SET SESSION optimizer_switch='loosescan=on';
+EXPLAIN
+SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
+SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
+
+set optimizer_switch= @tmp_otimizer_switch;
+
+DROP TABLE t1,t2,t3;
+
 # The following command must be the last one the file 
 set optimizer_switch=@subselect_sj_tmp;

sql/opt_subselect.h

@@ -170,7 +170,7 @@ class Loose_scan_opt
         PREV_BITS(ulonglong, s->emb_sj_nest->sj_in_exprs) &&     // (2)
         (PREV_BITS(key_part_map, max_loose_keypart+1) &        // (3)
          (found_part | loose_scan_keyparts)) ==                // (3)
-         (found_part | loose_scan_keyparts) &&                 // (3)
+        PREV_BITS(key_part_map, max_loose_keypart+1) &&        // (3)
         !key_uses_partial_cols(s->table, key))
     {
       /* Ok, can use the strategy */