Fix bug lp:856152

Analysis:
The cause of the bug was that the method
subselect_rowid_merge_engine::partial_match()
was not designed for re-execution within the
same query. Specifically, it didn't cleanup
the bitmap of matching keys after completion.

The test query requires double execution of
the IN predicate because it first checks the
predicate as a constant condition. The second
execution during regular execution used the bitmap
of matching keys produced by the first execution
instead of starting with a clean one.

Solution:
Cleanup the bitmap of matching keys at the end of
the partial matching procedure.

mysql-test/r/subselect_partial_match.result

@@ -348,4 +348,28 @@ c
 0
 0
 drop table t1, t2;
+#
+# LP BUG#856152 Wrong result with NOT IN subquery and partial_match_rowid_merge
+#
+CREATE TABLE t1 ( f1 integer NOT NULL , f2 integer) ;
+INSERT INTO t1 VALUES (3,3),(48,NULL),(49,1);
+CREATE TABLE t2 ( f3 int) ;
+INSERT INTO t2 VALUES (5);
+set @@optimizer_switch='in_to_exists=off,materialization=on,partial_match_rowid_merge=on,partial_match_table_scan=off';
+EXPLAIN SELECT * FROM t2 WHERE ( 3 , 1 ) NOT IN ( SELECT f1 , f2 FROM t1 );
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t2	system	NULL	NULL	NULL	NULL	1	
+2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	3	
+SELECT * FROM t2 WHERE ( 3 , 1 ) NOT IN ( SELECT f1 , f2 FROM t1 );
+f3
+5
+set @@optimizer_switch='in_to_exists=on,materialization=off';
+EXPLAIN SELECT * FROM t2 WHERE ( 3 , 1 ) NOT IN ( SELECT f1 , f2 FROM t1 );
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t2	system	NULL	NULL	NULL	NULL	1	
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+SELECT * FROM t2 WHERE ( 3 , 1 ) NOT IN ( SELECT f1 , f2 FROM t1 );
+f3
+5
+drop table t1, t2;
 set @@optimizer_switch=@save_optimizer_switch;

mysql-test/t/subselect_partial_match.test

@@ -354,4 +354,24 @@ SELECT * FROM t1 WHERE (6, 4 ) NOT IN (SELECT a, b FROM t2);
 
 drop table t1, t2;
 
+--echo #
+--echo # LP BUG#856152 Wrong result with NOT IN subquery and partial_match_rowid_merge
+--echo #
+
+CREATE TABLE t1 ( f1 integer NOT NULL , f2 integer) ;
+INSERT INTO t1 VALUES (3,3),(48,NULL),(49,1);
+
+CREATE TABLE t2 ( f3 int) ;
+INSERT INTO t2 VALUES (5);
+
+set @@optimizer_switch='in_to_exists=off,materialization=on,partial_match_rowid_merge=on,partial_match_table_scan=off';
+EXPLAIN SELECT * FROM t2 WHERE ( 3 , 1 ) NOT IN ( SELECT f1 , f2 FROM t1 );
+SELECT * FROM t2 WHERE ( 3 , 1 ) NOT IN ( SELECT f1 , f2 FROM t1 );
+
+set @@optimizer_switch='in_to_exists=on,materialization=off';
+EXPLAIN SELECT * FROM t2 WHERE ( 3 , 1 ) NOT IN ( SELECT f1 , f2 FROM t1 );
+SELECT * FROM t2 WHERE ( 3 , 1 ) NOT IN ( SELECT f1 , f2 FROM t1 );
+
+drop table t1, t2;
+
 set @@optimizer_switch=@save_optimizer_switch;

sql/item_subselect.cc

@@ -5674,6 +5674,8 @@ bool subselect_rowid_merge_engine::partial_match()
   DBUG_ASSERT(FALSE);
 
 end:
+  if (!has_covering_null_columns)
+    bitmap_clear_all(&matching_keys);
   queue_remove_all(&pq);
   tmp_table->file->ha_rnd_end();
   return res;