subselect.result, subselect.test:

  Added test cases for bug #7351.
item_cmpfunc.cc:
  Fixed bug #7351: incorrect result for a query with a
  subquery returning empty set.
  If in the predicate v IN (SELECT a FROM t WHERE cond)
  v is null, then the result of the predicate is either
  INKNOWN or FALSE. It is FALSE if the subquery returns
  an empty set.
item_subselect.cc:
  Fixed bug #7351: incorrect result for a query with a
  subquery returning empty set.
  The problem was due to not a quite legal transformation
  for 'IN' subqueries. A subquery containing a predicate
  of the form
  v IN (SELECT a FROM t WHERE cond)
  was transformed into
  EXISTS(SELECT a FROM t WHERE cond AND (a=v OR a IS NULL)).
  Yet, this transformation is valid only if v is not null.
  If v is null, then, in the case when
  (SELECT a FROM t WHERE cond) returns an empty set the value
  of the predicate is FALSE, otherwise the result of the
  predicate is INKNOWN.
  The fix resolves this problem by changing the result
  of the transformation to
  EXISTS(SELECT a FROM t WHERE cond AND (v IS NULL OR (a=v OR a IS NULL)))
  in the case when v is nullable.
  The new transformation prevents applying the lookup
  optimization for IN subqueries. To make it still
  applicable we have to introduce guarded access methods.

1 files changed, 20 insertions, 5 deletions

diff --git a/mysql-test/r/subselect.result b/mysql-test/r/subselect.result
index 0735f133e6f..b264018866c 100644
--- a/mysql-test/r/subselect.result
+++ b/mysql-test/r/subselect.result
@@ -1425,7 +1425,7 @@ Note	1003	(select test.t1.s1 AS `s1` from test.t1)
 s1
 tttt
 drop table t1;
-create table t1 (s1 char(5), index s1(s1));
+create table t1 (s1 char(5) not null, index s1(s1));
 create table t2 (s1 char(5), index s1(s1));
 insert into t1 values ('a1'),('a2'),('a3');
 insert into t2 values ('a1'),('a2');
@@ -1451,25 +1451,25 @@ a2	1
 a3	1
 explain extended select s1, s1 NOT IN (SELECT s1 FROM t2) from t1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	index	NULL	s1	6	NULL	3	Using index
+1	PRIMARY	t1	index	NULL	s1	5	NULL	3	Using index
 2	DEPENDENT SUBQUERY	t2	index_subquery	s1	s1	6	func	2	Using index
 Warnings:
 Note	1003	select test.t1.s1 AS `s1`,not(<in_optimizer>(test.t1.s1,<exists>(<index_lookup>(<cache>(test.t1.s1) in t2 on s1 chicking NULL)))) AS `s1 NOT IN (SELECT s1 FROM t2)` from test.t1
 explain extended select s1, s1 = ANY (SELECT s1 FROM t2) from t1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	index	NULL	s1	6	NULL	3	Using index
+1	PRIMARY	t1	index	NULL	s1	5	NULL	3	Using index
 2	DEPENDENT SUBQUERY	t2	index_subquery	s1	s1	6	func	2	Using index
 Warnings:
 Note	1003	select test.t1.s1 AS `s1`,<in_optimizer>(test.t1.s1,<exists>(<index_lookup>(<cache>(test.t1.s1) in t2 on s1 chicking NULL))) AS `s1 = ANY (SELECT s1 FROM t2)` from test.t1
 explain extended select s1, s1 <> ALL (SELECT s1 FROM t2) from t1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	index	NULL	s1	6	NULL	3	Using index
+1	PRIMARY	t1	index	NULL	s1	5	NULL	3	Using index
 2	DEPENDENT SUBQUERY	t2	index_subquery	s1	s1	6	func	2	Using index
 Warnings:
 Note	1003	select test.t1.s1 AS `s1`,not(<in_optimizer>(test.t1.s1,<exists>(<index_lookup>(<cache>(test.t1.s1) in t2 on s1 chicking NULL)))) AS `s1 <> ALL (SELECT s1 FROM t2)` from test.t1
 explain extended select s1, s1 NOT IN (SELECT s1 FROM t2 WHERE s1 < 'a2') from t1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	index	NULL	s1	6	NULL	3	Using index
+1	PRIMARY	t1	index	NULL	s1	5	NULL	3	Using index
 2	DEPENDENT SUBQUERY	t2	index_subquery	s1	s1	6	func	1	Using index; Using where
 Warnings:
 Note	1003	select test.t1.s1 AS `s1`,not(<in_optimizer>(test.t1.s1,<exists>(<index_lookup>(<cache>(test.t1.s1) in t2 on s1 chicking NULL where (test.t2.s1 < _latin1'a2'))))) AS `s1 NOT IN (SELECT s1 FROM t2 WHERE s1 < 'a2')` from test.t1
@@ -2125,3 +2125,18 @@ SELECT DISTINCT Continent AS c FROM t1 WHERE Code <> SOME ( SELECT Code FROM t1
 c
 Oceania
 drop table t1;
+CREATE TABLE t1 ( f1 BIGINT );
+INSERT INTO t1 SET f1= NULL;
+INSERT INTO t1 SET f1= 1;
+CREATE TABLE t2 ( f1 BIGINT );
+SELECT f1 FROM t1
+WHERE  f1 <> ALL ( SELECT f1 FROM t2 );
+f1
+NULL
+1
+INSERT INTO t2 VALUES (1), (2);
+SELECT f1 FROM t1
+WHERE f1 <> ALL ( SELECT f1 FROM t2 WHERE f1 > 2 );
+f1
+NULL
+1