Don't reset maybe_null in update_used_tables(); This breaks ROLLUP

This fixed failing test in group_by.test

mysql-test/r/join_outer.result:
  Updated test case
mysql-test/r/join_outer_jcl6.result:
  Updated test case
sql/item.cc:
  Don't reset maybe_null in update_used_tables(); This breaks ROLLUP
sql/item.h:
  Don't reset maybe_null in update_used_tables(); This breaks ROLLUP
sql/item_cmpfunc.h:
  Don't reset maybe_null in update_used_tables(); This breaks ROLLUP

mysql-test/r/join_outer.result

@@ -2019,10 +2019,10 @@ SELECT t1.pk FROM t2 LEFT JOIN t1 ON t2.pk = t1.a
 WHERE t1.b BETWEEN 5 AND 6 AND t1.pk IS NULL OR t1.pk = 5
 ORDER BY t1.pk;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	const	PRIMARY	PRIMARY	4	const	1	100.00	
+1	SIMPLE	t1	const	PRIMARY,idx	PRIMARY	4	const	1	100.00	
 1	SIMPLE	t2	const	PRIMARY	PRIMARY	4	const	1	100.00	Using index
 Warnings:
-Note	1003	select 5 AS `pk` from `test`.`t2` join `test`.`t1` where (1) order by 5
+Note	1003	select 5 AS `pk` from `test`.`t2` join `test`.`t1` where ((((1 between 5 and 6) and isnull(5)) or 1)) order by 5
 SELECT t1.pk FROM t2 LEFT JOIN t1 ON t2.pk = t1.a
 WHERE t1.b BETWEEN 5 AND 6 AND t1.pk IS NULL OR t1.pk = 5
 ORDER BY t1.pk;
@@ -2058,10 +2058,10 @@ SELECT t1.b, t2.c, t2.d FROM t2 LEFT JOIN t1 ON t2.c = t1.a
 WHERE t1.pk BETWEEN 5 AND 6 AND t1.b IS NULL OR t1.b = 5
 ORDER BY t1.b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	ref	idx	idx	4	const	2	100.00	Using where
+1	SIMPLE	t1	ref	PRIMARY,idx	idx	4	const	2	100.00	Using where; Using filesort
 1	SIMPLE	t2	ref	c	c	5	test.t1.a	2	100.00	
 Warnings:
-Note	1003	select `test`.`t1`.`b` AS `b`,`test`.`t2`.`c` AS `c`,`test`.`t2`.`d` AS `d` from `test`.`t2` join `test`.`t1` where ((`test`.`t2`.`c` = `test`.`t1`.`a`) and (`test`.`t1`.`b` = 5)) order by `test`.`t1`.`b`
+Note	1003	select `test`.`t1`.`b` AS `b`,`test`.`t2`.`c` AS `c`,`test`.`t2`.`d` AS `d` from `test`.`t2` join `test`.`t1` where ((`test`.`t2`.`c` = `test`.`t1`.`a`) and (((`test`.`t1`.`pk` between 5 and 6) and isnull(`test`.`t1`.`b`)) or (`test`.`t1`.`b` = 5))) order by `test`.`t1`.`b`
 SELECT t1.b, t2.c, t2.d FROM t2 LEFT JOIN t1 ON t2.c = t1.a
 WHERE t1.pk BETWEEN 5 AND 6 AND t1.b IS NULL OR t1.b = 5
 ORDER BY t1.b;

mysql-test/r/join_outer_jcl6.result

@@ -2030,10 +2030,10 @@ SELECT t1.pk FROM t2 LEFT JOIN t1 ON t2.pk = t1.a
 WHERE t1.b BETWEEN 5 AND 6 AND t1.pk IS NULL OR t1.pk = 5
 ORDER BY t1.pk;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	const	PRIMARY	PRIMARY	4	const	1	100.00	
+1	SIMPLE	t1	const	PRIMARY,idx	PRIMARY	4	const	1	100.00	
 1	SIMPLE	t2	const	PRIMARY	PRIMARY	4	const	1	100.00	Using index
 Warnings:
-Note	1003	select 5 AS `pk` from `test`.`t2` join `test`.`t1` where (1) order by 5
+Note	1003	select 5 AS `pk` from `test`.`t2` join `test`.`t1` where ((((1 between 5 and 6) and isnull(5)) or 1)) order by 5
 SELECT t1.pk FROM t2 LEFT JOIN t1 ON t2.pk = t1.a
 WHERE t1.b BETWEEN 5 AND 6 AND t1.pk IS NULL OR t1.pk = 5
 ORDER BY t1.pk;
@@ -2069,10 +2069,10 @@ SELECT t1.b, t2.c, t2.d FROM t2 LEFT JOIN t1 ON t2.c = t1.a
 WHERE t1.pk BETWEEN 5 AND 6 AND t1.b IS NULL OR t1.b = 5
 ORDER BY t1.b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	ref	idx	idx	4	const	2	100.00	Using where
+1	SIMPLE	t1	ref	PRIMARY,idx	idx	4	const	2	100.00	Using where; Using filesort
 1	SIMPLE	t2	ref	c	c	5	test.t1.a	2	100.00	
 Warnings:
-Note	1003	select `test`.`t1`.`b` AS `b`,`test`.`t2`.`c` AS `c`,`test`.`t2`.`d` AS `d` from `test`.`t2` join `test`.`t1` where ((`test`.`t2`.`c` = `test`.`t1`.`a`) and (`test`.`t1`.`b` = 5)) order by `test`.`t1`.`b`
+Note	1003	select `test`.`t1`.`b` AS `b`,`test`.`t2`.`c` AS `c`,`test`.`t2`.`d` AS `d` from `test`.`t2` join `test`.`t1` where ((`test`.`t2`.`c` = `test`.`t1`.`a`) and (((`test`.`t1`.`pk` between 5 and 6) and isnull(`test`.`t1`.`b`)) or (`test`.`t1`.`b` = 5))) order by `test`.`t1`.`b`
 SELECT t1.b, t2.c, t2.d FROM t2 LEFT JOIN t1 ON t2.c = t1.a
 WHERE t1.pk BETWEEN 5 AND 6 AND t1.b IS NULL OR t1.b = 5
 ORDER BY t1.b;

sql/item.cc

@@ -9603,7 +9603,7 @@ void Item_ref::update_used_tables()
 {
   if (!get_depended_from())
     (*ref)->update_used_tables();
-  maybe_null= (*ref)->maybe_null;
+  maybe_null|= (*ref)->maybe_null;
 }
 
 void Item_direct_view_ref::update_used_tables()

sql/item.h

@@ -2057,7 +2057,7 @@ public:
   {
     update_table_bitmaps();
     if (field && field->table)
-      maybe_null= field->maybe_null();
+      maybe_null|= field->maybe_null();
   }
   Item *get_tmp_table_item(THD *thd);
   bool collect_item_field_processor(uchar * arg);
@@ -3112,7 +3112,7 @@ public:
   void update_used_tables()
   {
     orig_item->update_used_tables();
-    maybe_null= orig_item->maybe_null;
+    maybe_null|= orig_item->maybe_null;
   }
   bool const_item() const { return orig_item->const_item(); }
   table_map not_null_tables() const { return orig_item->not_null_tables(); }

sql/item_cmpfunc.h

@@ -770,7 +770,7 @@ public:
   void update_used_tables()
   {
     Item_func_coalesce::update_used_tables();
-    maybe_null= args[1]->maybe_null;
+    maybe_null|= args[1]->maybe_null;
   }
   const char *func_name() const { return "ifnull"; }
   Field *tmp_table_field(TABLE *table);
@@ -797,7 +797,7 @@ public:
   void update_used_tables()
   {
     Item_func::update_used_tables();
-    maybe_null= args[1]->maybe_null || args[2]->maybe_null;
+    maybe_null|= args[1]->maybe_null || args[2]->maybe_null;
   }
   uint decimal_precision() const;
   const char *func_name() const { return "if"; }