* Bug #20792: Incorrect results from aggregate subquery

When processing aggregate functions all tables values are reset
to NULLs at the end of each group. 
When doing that if there are no rows found for a group
the const tables must not be reset as they are not recalculated 
by do_select()/sub_select() for each group.


mysql-test/r/subselect2.result:
  * Bug #20792: Incorrect results from aggregate subquery
   - test suite for the bug. This is dependent on InnoDB despite
     the fact that the bug and the fix are not InnoDB specific.
     This is because of the table flag HA_NOT_EXACT_COUNT.
     When this flag is off (as in MyISAM) both t2 and t3 become of
     join type 'system' as they are estimated to have 1 record and
     and this statistics can be trusted (according to the absence of
     HA_NOT_EXACT_COUNT).
mysql-test/t/subselect2.test:
  * Bug #20792: Incorrect results from aggregate subquery
   - test suite for the bug
sql/sql_select.cc:
  * Bug #20792: Incorrect results from aggregate subquery
   - when clearing results if there are not rows found for group
     the const tables must not be reset as they are not recalculated
     for each group.

1 files changed, 18 insertions, 0 deletions

diff --git a/mysql-test/t/subselect2.test b/mysql-test/t/subselect2.test
index b21eda176b6..162bdd0d90a 100644
--- a/mysql-test/t/subselect2.test
+++ b/mysql-test/t/subselect2.test
@@ -150,3 +150,21 @@ EXPLAIN SELECT t2.*, t4.DOCTYPENAME, t1.CONTENTSIZE,t1.MIMETYPE FROM t2 INNER JO
 
 drop table t1, t2, t3, t4;
 # End of 4.1 tests
+
+#
+# Bug #20792: Incorrect results from aggregate subquery
+#
+CREATE TABLE t1 (a int(10) , PRIMARY KEY (a)) Engine=InnoDB;
+INSERT INTO t1 VALUES (1),(2);
+
+CREATE TABLE t2 (a int(10), PRIMARY KEY (a)) Engine=InnoDB;
+INSERT INTO t2 VALUES (1);
+
+CREATE TABLE t3 (a int(10), b int(10), c int(10),
+                PRIMARY KEY (a)) Engine=InnoDB;
+INSERT INTO t3 VALUES (1,2,1);
+
+SELECT t1.* FROM t1 WHERE (SELECT COUNT(*) FROM t3,t2 WHERE t3.c=t2.a 
+                           and t2.a='1' AND t1.a=t3.b) > 0;
+
+DROP TABLE t1,t2,t3;