Fixed LP bug #887479.

The function setup_semijoin_dups_elimination erroneously assumed
that if join_cache_level is set to 3 or 4 then the type of the
access to a table cannot be JT_REF or JT_EQ_REF. This could lead
to wrong query result sets.

mysql-test/r/join_cache.result

@@ -5146,4 +5146,37 @@ a
 0
 SET SESSION join_cache_level = DEFAULT;
 DROP TABLE t1, t2;
+#
+# Bug #887479: join_cache_level=3 + semijoin=on 
+#
+CREATE TABLE t1 (a int, b int);
+INSERT INTO t1 VALUES (3914,17), (3710,5), (3888,20);
+CREATE TABLE t2 (c int, KEY (c));
+INSERT INTO t2 VALUES (27), (17), (33), (20), (3), (7), (18), (2);
+SET @tmp887479_optimizer_switch=@@optimizer_switch;
+SET SESSION optimizer_switch='semijoin=on';
+SET SESSION optimizer_switch='semijoin_with_cache=on';
+SET SESSION join_cache_level=1;
+EXPLAIN
+SELECT * FROM t1 WHERE (t1.b) IN (SELECT c FROM t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+1	PRIMARY	t2	ref	c	c	5	test.t1.b	2	Using index; Start temporary; End temporary
+SELECT * FROM t1 WHERE (t1.b) IN (SELECT c FROM t2);
+a	b
+3914	17
+3888	20
+SET SESSION join_cache_level=3;
+EXPLAIN
+SELECT * FROM t1 WHERE (t1.b) IN (SELECT c FROM t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where; Start temporary
+1	PRIMARY	t2	hash_index	c	#hash#c:c	5:5	test.t1.b	8	End temporary; Using join buffer (flat, BNLH join)
+SELECT * FROM t1 WHERE (t1.b) IN (SELECT c FROM t2);
+a	b
+3914	17
+3888	20
+SET SESSION join_cache_level = DEFAULT;
+SET optimizer_switch=@tmp887479_optimizer_switch;
+DROP TABLE t1,t2;
 set @@optimizer_switch=@save_optimizer_switch;

mysql-test/t/join_cache.test

@@ -3225,5 +3225,34 @@ SET SESSION join_cache_level = DEFAULT;
 
 DROP TABLE t1, t2;
 
+--echo #
+--echo # Bug #887479: join_cache_level=3 + semijoin=on 
+--echo #
+
+CREATE TABLE t1 (a int, b int);
+INSERT INTO t1 VALUES (3914,17), (3710,5), (3888,20);
+
+CREATE TABLE t2 (c int, KEY (c));
+INSERT INTO t2 VALUES (27), (17), (33), (20), (3), (7), (18), (2);
+
+SET @tmp887479_optimizer_switch=@@optimizer_switch;
+SET SESSION optimizer_switch='semijoin=on';
+SET SESSION optimizer_switch='semijoin_with_cache=on';
+
+SET SESSION join_cache_level=1;
+EXPLAIN
+SELECT * FROM t1 WHERE (t1.b) IN (SELECT c FROM t2);
+SELECT * FROM t1 WHERE (t1.b) IN (SELECT c FROM t2);
+
+SET SESSION join_cache_level=3;
+EXPLAIN
+SELECT * FROM t1 WHERE (t1.b) IN (SELECT c FROM t2);
+SELECT * FROM t1 WHERE (t1.b) IN (SELECT c FROM t2);
+
+SET SESSION join_cache_level = DEFAULT;
+SET optimizer_switch=@tmp887479_optimizer_switch;
+
+DROP TABLE t1,t2;
+
 # this must be the last command in the file
 set @@optimizer_switch=@save_optimizer_switch;

sql/opt_subselect.cc

@@ -3921,7 +3921,7 @@ int setup_semijoin_dups_elimination(JOIN *join, ulonglong options,
           if (j != join->const_tables && js_tab->use_quick != 2 &&
               j <= no_jbuf_after &&
               ((js_tab->type == JT_ALL && join_cache_level != 0) ||
-               (join_cache_level > 4 && (tab->type == JT_REF || 
+               (join_cache_level > 2 && (tab->type == JT_REF || 
                                          tab->type == JT_EQ_REF))))
           {
             /* Looks like we'll be using join buffer */