Bug#51598 Inconsistent behaviour with a COALESCE statement inside an IN comparison

Optimizer erroneously translated LEFT JOIN into INNER JOIN.
It leads to cutting rows with NULL right side. It happens
because Item_row uses not_null_tables() method form the
base(Item) class and does not calculate 'null tables'
properly. The fix is adding calculation of 'not null tables'
to Item_row.

mysql-test/r/join_outer.result

@@ -1289,3 +1289,23 @@ a	COUNT( t2.b )	SUM( t2.b )	MAX( t2.b )
 1	3	6	3
 NULL	3	6	3
 DROP TABLE t1, t2;
+#
+# Bug#51598 Inconsistent behaviour with a COALESCE statement inside an IN comparison
+#
+CREATE TABLE t1(f1 INT, f2 INT, f3 INT);
+INSERT INTO t1 VALUES (1, NULL, 3);
+CREATE TABLE t2(f1 INT, f2 INT);
+INSERT INTO t2 VALUES (2, 1);
+EXPLAIN EXTENDED SELECT * FROM t1 LEFT JOIN t2 ON t1.f2 = t2.f2
+WHERE (COALESCE(t1.f1, t2.f1), f3) IN ((1, 3), (2, 2));
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	100.00	
+1	SIMPLE	t2	system	NULL	NULL	NULL	NULL	1	100.00	
+Warnings:
+Note	1003	select '1' AS `f1`,NULL AS `f2`,'3' AS `f3`,NULL AS `f1`,NULL AS `f2` from `test`.`t1` left join `test`.`t2` on(multiple equal(NULL)) where ((coalesce('1',NULL),'3') in ((1,3),(2,2)))
+SELECT * FROM t1 LEFT JOIN t2 ON t1.f2 = t2.f2
+WHERE (COALESCE(t1.f1, t2.f1), f3) IN ((1, 3), (2, 2));
+f1	f2	f3	f1	f2
+1	NULL	3	NULL	NULL
+DROP TABLE t1, t2;
+End of 5.1 tests

mysql-test/t/join_outer.test

@@ -896,3 +896,21 @@ FROM t1 JOIN t2 USING( a )
 GROUP BY t1.a WITH ROLLUP;
 
 DROP TABLE t1, t2;
+
+--echo #
+--echo # Bug#51598 Inconsistent behaviour with a COALESCE statement inside an IN comparison
+--echo #
+CREATE TABLE t1(f1 INT, f2 INT, f3 INT);
+INSERT INTO t1 VALUES (1, NULL, 3);
+CREATE TABLE t2(f1 INT, f2 INT);
+INSERT INTO t2 VALUES (2, 1);
+
+EXPLAIN EXTENDED SELECT * FROM t1 LEFT JOIN t2 ON t1.f2 = t2.f2
+WHERE (COALESCE(t1.f1, t2.f1), f3) IN ((1, 3), (2, 2));
+
+SELECT * FROM t1 LEFT JOIN t2 ON t1.f2 = t2.f2
+WHERE (COALESCE(t1.f1, t2.f1), f3) IN ((1, 3), (2, 2));
+
+DROP TABLE t1, t2;
+
+--echo End of 5.1 tests

sql/item_row.cc

@@ -30,7 +30,8 @@
 */
 
 Item_row::Item_row(List<Item> &arg):
-  Item(), used_tables_cache(0), const_item_cache(1), with_null(0)
+  Item(), used_tables_cache(0), not_null_tables_cache(0),
+  const_item_cache(1), with_null(0)
 {
 
   //TODO: think placing 2-3 component items in item (as it done for function)
@@ -71,6 +72,7 @@ bool Item_row::fix_fields(THD *thd, Item **ref)
     Item *item= *arg;
     used_tables_cache |= item->used_tables();
     const_item_cache&= item->const_item() && !with_null;
+    not_null_tables_cache|= item->not_null_tables();
     /*
       Some subqueries transformations aren't done in the view_prepare_mode thus
       is_null() will fail. So we skip is_null() calculation for CREATE VIEW as

sql/item_row.h

@@ -16,7 +16,7 @@
 class Item_row: public Item
 {
   Item **items;
-  table_map used_tables_cache;
+  table_map used_tables_cache, not_null_tables_cache;
   uint arg_count;
   bool const_item_cache;
   bool with_null;
@@ -26,6 +26,7 @@ class Item_row: public Item
     Item(),
     items(item->items),
     used_tables_cache(item->used_tables_cache),
+    not_null_tables_cache(0),
     arg_count(item->arg_count),
     const_item_cache(item->const_item_cache),
     with_null(0)
@@ -65,6 +66,7 @@ class Item_row: public Item
   bool const_item() const { return const_item_cache; };
   enum Item_result result_type() const { return ROW_RESULT; }
   void update_used_tables();
+  table_map not_null_tables() const { return not_null_tables_cache; }
   virtual void print(String *str, enum_query_type query_type);
 
   bool walk(Item_processor processor, bool walk_subquery, uchar *arg);