subselect.result, subselect.test:

  Added a test case for bug #9516.
item_subselect.h:
  Fixed bug #9516.
  The bug was due to that fact that the class Item_subselect
  inherited the generic implementation of the function
  not_null_tables that was not valid for the objects
  of this class. As a result evaluation of the
  not_null_tables attribute was not correct for subqueries.
  This caused invalid transformations of outer joins into
  inner joins.

mysql-test/r/subselect.result

@@ -2762,3 +2762,22 @@ WHERE c2 IN ( SELECT c2 FROM t2 WHERE c2 IN ( 1 ) );
 c1	c2
 1	1
 DROP TABLE t1,t2;
+CREATE TABLE t1 ( c1 integer );
+INSERT INTO t1 VALUES ( 1 );
+INSERT INTO t1 VALUES ( 2 );
+INSERT INTO t1 VALUES ( 3 );
+INSERT INTO t1 VALUES ( 6 );
+CREATE TABLE t2 ( c2 integer );
+INSERT INTO t2 VALUES ( 1 );
+INSERT INTO t2 VALUES ( 4 );
+INSERT INTO t2 VALUES ( 5 );
+INSERT INTO t2 VALUES ( 6 );
+CREATE TABLE t3 ( c3 integer );
+INSERT INTO t3 VALUES ( 7 );
+INSERT INTO t3 VALUES ( 8 );
+SELECT c1,c2 FROM t1 LEFT JOIN t2 ON c1 = c2 
+WHERE EXISTS (SELECT c3 FROM t3 WHERE c2 IS NULL );
+c1	c2
+2	NULL
+3	NULL
+DROP TABLE t1,t2,t3;

mysql-test/t/subselect.test

@@ -1773,3 +1773,29 @@ SELECT * FROM t1 LEFT JOIN t2 ON c1 = c2
   WHERE c2 IN ( SELECT c2 FROM t2 WHERE c2 IN ( 1 ) );
 
 DROP TABLE t1,t2;
+
+#
+# Test for bug #9516: wrong evaluation of not_null_tables attribute in SQ 
+#
+
+CREATE TABLE t1 ( c1 integer );
+INSERT INTO t1 VALUES ( 1 );
+INSERT INTO t1 VALUES ( 2 );
+INSERT INTO t1 VALUES ( 3 );
+INSERT INTO t1 VALUES ( 6 ); 
+ 
+CREATE TABLE t2 ( c2 integer );
+INSERT INTO t2 VALUES ( 1 );
+INSERT INTO t2 VALUES ( 4 );
+INSERT INTO t2 VALUES ( 5 );
+INSERT INTO t2 VALUES ( 6 );
+
+CREATE TABLE t3 ( c3 integer );
+INSERT INTO t3 VALUES ( 7 );
+INSERT INTO t3 VALUES ( 8 );
+
+SELECT c1,c2 FROM t1 LEFT JOIN t2 ON c1 = c2 
+  WHERE EXISTS (SELECT c3 FROM t3 WHERE c2 IS NULL );
+
+DROP TABLE t1,t2,t3;
+

sql/item_subselect.h

@@ -96,6 +96,7 @@ class Item_subselect :public Item_result_field
   virtual bool exec();
   virtual void fix_length_and_dec();
   table_map used_tables() const;
+  table_map not_null_tables() const { return 0; }
   bool const_item() const;
   inline table_map get_used_tables_cache() { return used_tables_cache; }
   inline bool get_const_item_cache() { return const_item_cache; }