Fixed bug #15347: Wrong result of subselect when records cache and set

functions are involved.

When subselect is a join with set functions and no record have been found in
it, end_send_group() sets null_row for all tables in order aggregate functions 
to calculate their values correctly. Normally this null_row flag is cleared for 
each table in sub_select(), but flush_cached_records() doesn't do so.
Due to this all fields from the table processed by flush_cached_records() are 
always evaluated as nulls and whole select produces wrong result.

flush_cached_records() now clears null_row flag at the very beginning.

mysql-test/r/select.result

@@ -3337,3 +3337,14 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t2	const	PRIMARY	PRIMARY	4	const	1	Using index
 1	SIMPLE	t3	const	PRIMARY	PRIMARY	8	const,const	1	
 DROP TABLE t1,t2,t3;
+create  table t1 (f1 int);
+insert into t1 values(1),(2);
+create table t2 (f2 int, f3 int, key(f2));
+insert into t2 values(1,1),(2,2);
+create table t3 (f4 int not null);
+insert into t3 values (2),(2),(2);
+select f1,(select count(*) from t2,t3 where f2=f1 and f3=f4) as count from t1;
+f1	count
+1	0
+2	3
+drop table t1,t2,t3;

mysql-test/t/select.test

@@ -2805,3 +2805,16 @@ EXPLAIN SELECT t2.key_a,foo
     WHERE t2.key_a=2 and key_b=5;
 
 DROP TABLE t1,t2,t3;
+
+#
+# Bug#15347 Wrong result of subselect when records cache and set functions
+#           are involved
+#
+create  table t1 (f1 int);
+insert into t1 values(1),(2);
+create table t2 (f2 int, f3 int, key(f2));
+insert into t2 values(1,1),(2,2);
+create table t3 (f4 int not null);
+insert into t3 values (2),(2),(2);
+select f1,(select count(*) from t2,t3 where f2=f1 and f3=f4) as count from t1;
+drop table t1,t2,t3;

sql/sql_select.cc

@@ -9853,6 +9853,7 @@ flush_cached_records(JOIN *join,JOIN_TAB *join_tab,bool skip_last)
   int error;
   READ_RECORD *info;
 
+  join_tab->table->null_row= 0;
   if (!join_tab->cache.records)
     return NESTED_LOOP_OK;                      /* Nothing to do */
   if (skip_last)