Fixed LP bug #823826.

The method Item_func_isnull::update_used_tables() erroneously did not
update cached values stored in the fields used_tables_cache and
const_item_cache of the Item_func_isnull objects. As a result the
Item_func_isnull::used_tables() returned wrong bitmaps and, as a
consequence, push-down predicates could be attached to wrong tables.

mysql-test/r/derived_view.result

@@ -1214,5 +1214,33 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 SELECT * FROM (SELECT * FROM (SELECT @b) AS t) AS s;
 @b
 NULL
-set optimizer_switch=@exit_optimizer_switch;
+set optimizer_switch='derived_merge=on';
+#
+# LP bug #823826: view over join + IS NULL in WHERE
+#
+CREATE TABLE t1 (a int) ;
+INSERT INTO t1 VALUES (1), (1);
+CREATE TABLE t2 (b int) ;
+INSERT INTO t2 VALUES (9), (NULL), (7);
+CREATE VIEW v1 AS SELECT * FROM t1,t2;
+EXPLAIN
+SELECT * FROM (SELECT * FROM t1,t2) t WHERE b IS NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	3	Using where; Using join buffer (flat, BNL join)
+SELECT * FROM (SELECT * FROM t1,t2) t WHERE b IS NULL;
+a	b
+1	NULL
+1	NULL
+EXPLAIN
+SELECT * FROM v1 WHERE b IS NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	3	Using where; Using join buffer (flat, BNL join)
+SELECT * FROM v1 WHERE b IS NULL;
+a	b
+1	NULL
+1	NULL
+DROP VIEW v1;
+DROP TABLE t1,t2;
 set optimizer_switch=@exit_optimizer_switch;

mysql-test/t/derived_view.test

@@ -735,7 +735,30 @@ set optimizer_switch='derived_merge=off';
 EXPLAIN
 SELECT * FROM (SELECT * FROM (SELECT @b) AS t) AS s;
 SELECT * FROM (SELECT * FROM (SELECT @b) AS t) AS s;
-set optimizer_switch=@exit_optimizer_switch;
+set optimizer_switch='derived_merge=on';
+
+--echo #
+--echo # LP bug #823826: view over join + IS NULL in WHERE
+--echo #
+
+CREATE TABLE t1 (a int) ;
+INSERT INTO t1 VALUES (1), (1);
+
+CREATE TABLE t2 (b int) ;
+INSERT INTO t2 VALUES (9), (NULL), (7);
+
+CREATE VIEW v1 AS SELECT * FROM t1,t2;
+
+EXPLAIN
+SELECT * FROM (SELECT * FROM t1,t2) t WHERE b IS NULL;
+SELECT * FROM (SELECT * FROM t1,t2) t WHERE b IS NULL;
+
+EXPLAIN
+SELECT * FROM v1 WHERE b IS NULL;
+SELECT * FROM v1 WHERE b IS NULL;
+
+DROP VIEW v1;
+DROP TABLE t1,t2;
 
 # The following command must be the last one the file 
 set optimizer_switch=@exit_optimizer_switch;

sql/item_cmpfunc.h

@@ -1365,7 +1365,11 @@ public:
       const_item_cache= 1;
     }
     else
+    {
       args[0]->update_used_tables();
+      used_tables_cache= args[0]->used_tables();
+      const_item_cache= args[0]->const_item();
+    }
   }
   table_map not_null_tables() const { return 0; }
   optimize_type select_optimize() const { return OPTIMIZE_NULL; }