MDEV-19778 Wrong Result on Left Outer Join with Subquery right on true

and WHERE filter afterwards

This patch complements the patch fixing the bug MDEV-6892. The latter
properly handled queries that used mergeable views returning constant
columns as inner tables of outer joins and whose where clause contained
predicates referring to these columns if the predicates of happened not
to be equality predicates. Otherwise the server still could return wrong
result sets for such queries. Besides the fix for MDEV-6892 prevented
some possible conversions of outer joins to inner joins for such queries.

This patch corrected the function check_simple_equality() to handle
properly conjunctive equalities of the where clause that refer to the
constant columns of mergeable views used as inner tables of an outer join.
The patch also changed the code of Item_direct_view_ref::not_null_tables().
This change allowed to take into account predicates containing references
to constant columns of mergeable views when converting outer joins into
inner joins.

mysql-test/r/derived.result

@@ -578,6 +578,15 @@ select x.id, message from (select id from t1) x left join
 (select id, 1 as message from t2) y on x.id=y.id
 where coalesce(message,0) <> 0;
 id	message
+explain extended
+select x.id, message from (select id from t1) x left join
+(select id, 1 as message from t2) y on x.id=y.id
+where message <> 0;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where; Using join buffer (flat, BNL join)
+Warnings:
+Note	1003	select `test`.`t1`.`id` AS `id`,1 AS `message` from `test`.`t1` join `test`.`t2` where (`test`.`t2`.`id` = `test`.`t1`.`id`)
 drop table t1,t2;
 #
 # MDEV-7827: Assertion `!table || (!table->read_set ||

mysql-test/r/derived_view.result

@@ -3041,3 +3041,60 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 7	DERIVED	p9	ALL	NULL	NULL	NULL	NULL	550	Using where; Using join buffer (incremental, BNL join)
 7	DERIVED	p10	ALL	NULL	NULL	NULL	NULL	550	Using where; Using join buffer (incremental, BNL join)
 DROP TABLE  t1, t2;
+#
+# MDEV-19778: equality condition for mergeable view returning constants
+#             in its columns and used as inner table of outer join
+#
+create table t1 (pk int, a int);
+insert into t1 values (1,7), (2,3), (3,2), (4,3);
+create table t2 (b int);
+insert into t2 values (5), (1), (NULL), (3);
+create table t3 (c int);
+insert into t3 values (1), (8);
+create view v1 as
+select 3 as d, t2.b from t2;
+select * from t1 left join v1 on t1.pk <= 2 where t1.a=v1.d;
+pk	a	d	b
+2	3	3	5
+2	3	3	1
+2	3	3	NULL
+2	3	3	3
+explain extended select * from t1 left join v1 on t1.pk <= 2 where t1.a=v1.d;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	100.00	Using where
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	4	100.00	Using join buffer (flat, BNL join)
+Warnings:
+Note	1003	select `test`.`t1`.`pk` AS `pk`,`test`.`t1`.`a` AS `a`,3 AS `d`,`test`.`t2`.`b` AS `b` from `test`.`t1` join `test`.`t2` where ((`test`.`t1`.`a` = 3) and (`test`.`t1`.`pk` <= 2))
+select * from t1 left join (select 3 as d, t2.b from t2) dt on t1.pk <= 2
+where t1.a=dt.d;
+pk	a	d	b
+2	3	3	5
+2	3	3	1
+2	3	3	NULL
+2	3	3	3
+explain extended select * from t1 left join (select 3 as d, t2.b from t2) dt on t1.pk <= 2
+where t1.a=dt.d;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	100.00	Using where
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	4	100.00	Using join buffer (flat, BNL join)
+Warnings:
+Note	1003	select `test`.`t1`.`pk` AS `pk`,`test`.`t1`.`a` AS `a`,3 AS `d`,`test`.`t2`.`b` AS `b` from `test`.`t1` join `test`.`t2` where ((`test`.`t1`.`a` = 3) and (`test`.`t1`.`pk` <= 2))
+select * from t1 left join (v1,t3) on t1.pk <= 2 where t1.a=v1.d;
+pk	a	d	b	c
+2	3	3	5	1
+2	3	3	5	8
+2	3	3	1	1
+2	3	3	1	8
+2	3	3	NULL	1
+2	3	3	NULL	8
+2	3	3	3	1
+2	3	3	3	8
+explain extended select * from t1 left join (v1,t3) on t1.pk <= 2 where t1.a=v1.d;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	2	100.00	
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	100.00	Using where; Using join buffer (flat, BNL join)
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	4	100.00	Using join buffer (incremental, BNL join)
+Warnings:
+Note	1003	select `test`.`t1`.`pk` AS `pk`,`test`.`t1`.`a` AS `a`,3 AS `d`,`test`.`t2`.`b` AS `b`,`test`.`t3`.`c` AS `c` from `test`.`t1` join `test`.`t2` join `test`.`t3` where ((`test`.`t1`.`a` = 3) and (`test`.`t1`.`pk` <= 2))
+drop view v1;
+drop table t1,t2,t3;

mysql-test/r/func_group.result

@@ -1981,6 +1981,7 @@ NULL
 Warnings:
 Warning	1292	Truncated incorrect INTEGER value: 'j'
 Warning	1292	Truncated incorrect INTEGER value: 'j'
+Warning	1292	Truncated incorrect INTEGER value: 'j'
 
 EXPLAIN
 SELECT MIN(t2.pk)
@@ -1995,6 +1996,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 Warnings:
 Warning	1292	Truncated incorrect INTEGER value: 'j'
 Warning	1292	Truncated incorrect INTEGER value: 'j'
+Warning	1292	Truncated incorrect INTEGER value: 'j'
 
 #
 # 2) Test that subquery materialization is setup for query with

mysql-test/r/subselect_cache.result

@@ -3130,6 +3130,7 @@ WHERE table1 .`col_varchar_key` )	field10
 Warnings:
 Warning	1292	Truncated incorrect DOUBLE value: 'f'
 Warning	1292	Truncated incorrect DOUBLE value: 'f'
+Warning	1292	Truncated incorrect DOUBLE value: 'f'
 SET @@optimizer_switch = 'subquery_cache=on';
 /* cache is on */ SELECT COUNT( DISTINCT table2 .`col_int_key` ) , (
 SELECT SUBQUERY2_t1 .`col_int_key`
@@ -3146,6 +3147,7 @@ WHERE table1 .`col_varchar_key` )	field10
 Warnings:
 Warning	1292	Truncated incorrect DOUBLE value: 'f'
 Warning	1292	Truncated incorrect DOUBLE value: 'f'
+Warning	1292	Truncated incorrect DOUBLE value: 'f'
 drop table t1,t2,t3,t4;
 set @@optimizer_switch= default;
 #launchpad BUG#611625

mysql-test/t/derived.test

@@ -502,6 +502,10 @@ insert into t2 values(4),(5),(6);
 select x.id, message from (select id from t1) x left join
 (select id, 1 as message from t2) y on x.id=y.id
 where coalesce(message,0) <> 0;
+explain extended
+select x.id, message from (select id from t1) x left join
+(select id, 1 as message from t2) y on x.id=y.id
+where message <> 0;
 drop table t1,t2;
 
 --echo #

mysql-test/t/derived_view.test

@@ -2194,3 +2194,37 @@ JOIN
  ) gp_20 ON gp_20.id=t2.id ;
 
 DROP TABLE  t1, t2;
+
+--echo #
+--echo # MDEV-19778: equality condition for mergeable view returning constants
+--echo #             in its columns and used as inner table of outer join
+--echo #
+
+create table t1 (pk int, a int);
+insert into t1 values (1,7), (2,3), (3,2), (4,3);
+create table t2 (b int);
+insert into t2 values (5), (1), (NULL), (3);
+create table t3 (c int);
+insert into t3 values (1), (8);
+
+create view v1 as
+select 3 as d, t2.b from t2;
+
+let $q=
+select * from t1 left join v1 on t1.pk <= 2 where t1.a=v1.d;
+eval $q;
+eval explain extended $q;
+
+let $q=
+select * from t1 left join (select 3 as d, t2.b from t2) dt on t1.pk <= 2
+  where t1.a=dt.d;
+eval $q;
+eval explain extended $q;
+
+let $q=
+select * from t1 left join (v1,t3) on t1.pk <= 2 where t1.a=v1.d;
+eval $q;
+eval explain extended $q;
+
+drop view v1;
+drop table t1,t2,t3;

sql/item.cc

@@ -9814,11 +9814,14 @@ table_map Item_direct_view_ref::used_tables() const
 
 table_map Item_direct_view_ref::not_null_tables() const
 {
-  return get_depended_from() ?
+  if (get_depended_from())
-         0 :
+    return 0;
-         ((view->is_merged_derived() || view->merged || !view->table) ?
+  if  (!( view->merged || !view->table))
-          (*ref)->not_null_tables() :
+    return view->table->map;
-          view->table->map);
+  TABLE *tab= get_null_ref_table();
+  if (tab == NO_NULL_TABLE || (*ref)->used_tables())
+    return (*ref)->not_null_tables();
+   return get_null_ref_table()->map;
 }
 
 /*

sql/item.h

@@ -3382,6 +3382,7 @@ public:
   void update_used_tables();
   table_map not_null_tables() const;
   bool const_item() const { return used_tables() == 0; }
+  TABLE *get_null_ref_table() const { return null_ref_table; }
   bool walk(Item_processor processor, bool walk_subquery, uchar *arg)
   { 
     return (*ref)->walk(processor, walk_subquery, arg) ||

sql/item_func.cc

@@ -226,6 +226,7 @@ Item_func::fix_fields(THD *thd, Item **ref)
       with_field= with_field || item->with_field;
       used_tables_cache|=     item->used_tables();
       const_item_cache&=      item->const_item();
+      not_null_tables_cache|= item->not_null_tables();
       with_subselect|=        item->has_subquery();
     }
   }

sql/sql_select.cc

@@ -1030,7 +1030,6 @@ JOIN::optimize()
       DBUG_RETURN(1); /* purecov: inspected */
     /* dump_TABLE_LIST_graph(select_lex, select_lex->leaf_tables); */
     select_lex->update_used_tables();
-
   }
   
   eval_select_list_used_tables();
@@ -1092,6 +1091,8 @@ JOIN::optimize()
 
     sel->where= conds;
 
+    select_lex->update_used_tables();
+
     if (arena)
       thd->restore_active_arena(arena, &backup);
   }
@@ -11763,6 +11764,9 @@ static bool check_simple_equality(Item *left_item, Item *right_item,
   {
     if (((Item_ref*)left_item)->get_depended_from())
       return FALSE;
+    if (((Item_direct_view_ref*)left_item)->get_null_ref_table() !=
+        NO_NULL_TABLE && !left_item->real_item()->used_tables())
+      return FALSE;
     left_item= left_item->real_item();
   }
   if (right_item->type() == Item::REF_ITEM &&
@@ -11770,6 +11774,9 @@ static bool check_simple_equality(Item *left_item, Item *right_item,
   {
     if (((Item_ref*)right_item)->get_depended_from())
       return FALSE;
+    if (((Item_direct_view_ref*)right_item)->get_null_ref_table() !=
+        NO_NULL_TABLE && !right_item->real_item()->used_tables())
+      return FALSE;
     right_item= right_item->real_item();
   }
   if (left_item->type() == Item::FIELD_ITEM &&