Merge from bk:ysql-next-mr-bugfixing.

mysql-test/r/subselect3.result

@@ -964,3 +964,53 @@ Variable_name	Value
 Handler_read_rnd_next	18
 DROP TABLE t1,t2;
 End of 5.1 tests
+#
+# BUG#48920: COUNT DISTINCT returns 1 for NULL values when in a subquery 
+#            in the select list
+#
+
+CREATE TABLE t1 (
+i int(11) DEFAULT NULL,
+v varchar(1) DEFAULT NULL
+);
+
+INSERT INTO t1 VALUES (8,'v');
+INSERT INTO t1 VALUES (9,'r');
+INSERT INTO t1 VALUES (NULL,'y');
+
+CREATE TABLE t2 (
+i int(11) DEFAULT NULL,
+v varchar(1) DEFAULT NULL,
+KEY i_key (i)
+);
+
+INSERT INTO t2 VALUES (NULL,'r');
+INSERT INTO t2 VALUES (0,'c');
+INSERT INTO t2 VALUES (0,'o');
+INSERT INTO t2 VALUES (2,'v');
+INSERT INTO t2 VALUES (7,'c');
+
+SELECT i, v, (SELECT COUNT(DISTINCT i)
+FROM t1
+WHERE v  = t2.v) as subsel
+FROM t2;
+i	v	subsel
+NULL	r	1
+0	c	0
+0	o	0
+2	v	1
+7	c	0
+
+EXPLAIN EXTENDED
+SELECT i, v, (SELECT COUNT(DISTINCT i)
+FROM t1
+WHERE v  = t2.v) as subsel
+FROM t2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	5	100.00	
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where
+Warnings:
+Note	1276	Field or reference 'test.t2.v' of SELECT #2 was resolved in SELECT #1
+Note	1003	select `test`.`t2`.`i` AS `i`,`test`.`t2`.`v` AS `v`,(select count(distinct `test`.`t1`.`i`) AS `COUNT(DISTINCT i)` from `test`.`t1` where (`test`.`t1`.`v` = `test`.`t2`.`v`)) AS `subsel` from `test`.`t2`
+DROP TABLE t1,t2;
+End of 5.6 tests

mysql-test/t/subselect3.test

@@ -794,3 +794,50 @@ SHOW STATUS LIKE '%Handler_read_rnd_next';
 DROP TABLE t1,t2;
 
 --echo End of 5.1 tests
+
+--echo #
+--echo # BUG#48920: COUNT DISTINCT returns 1 for NULL values when in a subquery 
+--echo #            in the select list
+--echo #
+
+--echo 
+CREATE TABLE t1 (
+  i int(11) DEFAULT NULL,
+  v varchar(1) DEFAULT NULL
+);
+
+--echo 
+INSERT INTO t1 VALUES (8,'v');
+INSERT INTO t1 VALUES (9,'r');
+INSERT INTO t1 VALUES (NULL,'y');
+
+--echo 
+CREATE TABLE t2 (
+  i int(11) DEFAULT NULL,
+  v varchar(1) DEFAULT NULL,
+  KEY i_key (i)
+);
+
+--echo 
+INSERT INTO t2 VALUES (NULL,'r');
+INSERT INTO t2 VALUES (0,'c');
+INSERT INTO t2 VALUES (0,'o');
+INSERT INTO t2 VALUES (2,'v');
+INSERT INTO t2 VALUES (7,'c');
+
+--echo 
+SELECT i, v, (SELECT COUNT(DISTINCT i)
+              FROM t1
+              WHERE v  = t2.v) as subsel
+FROM t2;
+
+--echo 
+EXPLAIN EXTENDED
+SELECT i, v, (SELECT COUNT(DISTINCT i)
+              FROM t1
+              WHERE v  = t2.v) as subsel
+FROM t2;
+
+DROP TABLE t1,t2;
+
+--echo End of 5.6 tests

sql/item_sum.cc

@@ -578,7 +578,14 @@ int Item_sum::set_aggregator(Aggregator::Aggregator_type aggregator)
 {
   if (aggr)
   {
+    /* 
+      Dependent subselects may be executed multiple times, making
+      set_aggregator to be called multiple times. The aggregator type
+      will be the same, but it needs to be reset so that it is
+      reevaluated with the new dependent data.
+    */
     DBUG_ASSERT(aggregator == aggr->Aggrtype());
+    aggr->clear();
     return FALSE;
   }
   switch (aggregator)