avoid null check on fields where NULL is impossible

(BUG#2393)


mysql-test/r/subselect.result:
  BUG#2393 test suite
  test ref replaced ref_of_null joining
mysql-test/t/subselect.test:
  BUG#2393 test suite
  test ref replaced ref_of_null joining
sql/item_subselect.cc:
  avoid null check on fields where NULL is impossible
sql/sql_select.cc:
  convert JT_REF_OR_NULL to JT_REF in case of impossible NULL and protect buffer of rewriting through join_tab->null_ref_key

mysql-test/r/subselect.result

@@ -1625,3 +1625,59 @@ PIPPO
 1
 NULL
 DROP TABLE t1, t2;
+create table t1 (id int not null, text varchar(20) not null default '', primary key (id));
+insert into t1 (id, text) values (1, 'text1'), (2, 'text2'), (3, 'text3'), (4, 'text4'), (5, 'text5'), (6, 'text6'), (7, 'text7'), (8, 'text8'), (9, 'text9'), (10, 'text10'), (11, 'text11'), (12, 'text12');
+select * from t1 where id not in (select id from t1 where id < 8);
+id	text
+8	text8
+9	text9
+10	text10
+11	text11
+12	text12
+select * from t1 as tt where not exists (select id from t1 where id < 8 and (id = tt.id or id is null) having id is not null);
+id	text
+8	text8
+9	text9
+10	text10
+11	text11
+12	text12
+explain extended select * from t1 where id not in (select id from t1 where id < 8);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	12	Using where
+2	DEPENDENT SUBQUERY	t1	unique_subquery	PRIMARY	PRIMARY	4	func	1	Using index; Using where
+Warnings:
+Note	1003	select high_priority test.t1.id AS `id`,test.t1.text AS `text` from test.t1 where not(<in_optimizer>(test.t1.id,<exists>(<primary_index_lookup>(<cache>(test.t1.id) in t1 on PRIMARY where (test.t1.id < 8)))))
+explain extended select * from t1 as tt where not exists (select id from t1 where id < 8 and (id = tt.id or id is null) having id is not null);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	tt	ALL	NULL	NULL	NULL	NULL	12	Using where
+2	DEPENDENT SUBQUERY	t1	eq_ref	PRIMARY	PRIMARY	4	test.tt.id	7	Using where; Using index
+Warnings:
+Note	1275	Field or reference 'tt.id' of SELECT #2 was resolved in SELECT #1
+Note	1003	select high_priority test.tt.id AS `id`,test.tt.text AS `text` from test.t1 tt where not(exists(select test.t1.id AS `id` from test.t1 where ((test.t1.id < 8) and ((test.t1.id = test.tt.id) or isnull(test.t1.id))) having (test.t1.id is not null) limit 1))
+insert into t1 (id, text) values (1000, 'text1000'), (1001, 'text1001');
+create table t2 (id int not null, text varchar(20) not null default '', primary key (id));
+insert into t2 (id, text) values (1, 'text1'), (2, 'text2'), (3, 'text3'), (4, 'text4'), (5, 'text5'), (6, 'text6'), (7, 'text7'), (8, 'text8'), (9, 'text9'), (10, 'text10'), (11, 'text1'), (12, 'text2'), (13, 'text3'), (14, 'text4'), (15, 'text5'), (16, 'text6'), (17, 'text7'), (18, 'text8'), (19, 'text9'), (20, 'text10'),(21, 'text1'), (22, 'text2'), (23, 'text3'), (24, 'text4'), (25, 'text5'), (26, 'text6'), (27, 'text7'), (28, 'text8'), (29, 'text9'), (30, 'text10'), (31, 'text1'), (32, 'text2'), (33, 'text3'), (34, 'text4'), (35, 'text5'), (36, 'text6'), (37, 'text7'), (38, 'text8'), (39, 'text9'), (40, 'text10'), (41, 'text1'), (42, 'text2'), (43, 'text3'), (44, 'text4'), (45, 'text5'), (46, 'text6'), (47, 'text7'), (48, 'text8'), (49, 'text9'), (50, 'text10');
+select * from t1 a left join t2 b on (a.id=b.id or b.id is null) join t1 c on (if(isnull(b.id), 1000, b.id)=c.id);
+id	text	id	text	id	text
+1	text1	1	text1	1	text1
+2	text2	2	text2	2	text2
+3	text3	3	text3	3	text3
+4	text4	4	text4	4	text4
+5	text5	5	text5	5	text5
+6	text6	6	text6	6	text6
+7	text7	7	text7	7	text7
+8	text8	8	text8	8	text8
+9	text9	9	text9	9	text9
+10	text10	10	text10	10	text10
+11	text11	11	text1	11	text11
+12	text12	12	text2	12	text12
+1000	text1000	NULL	NULL	1000	text1000
+1001	text1001	NULL	NULL	1000	text1000
+explain extended select * from t1 a left join t2 b on (a.id=b.id or b.id is null) join t1 c on (if(isnull(b.id), 1000, b.id)=c.id);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	a	ALL	NULL	NULL	NULL	NULL	14	
+1	SIMPLE	b	eq_ref	PRIMARY	PRIMARY	4	test.a.id	2	
+1	SIMPLE	c	eq_ref	PRIMARY	PRIMARY	4	func	1	Using where
+Warnings:
+Note	1003	select high_priority test.a.id AS `id`,test.a.text AS `text`,test.b.id AS `id`,test.b.text AS `text`,test.c.id AS `id`,test.c.text AS `text` from test.t1 a left join test.t2 b on(((test.a.id = test.b.id) or isnull(test.b.id))) join test.t1 c where (if(isnull(test.b.id),1000,test.b.id) = test.c.id)
+drop table t1,t2;

mysql-test/t/subselect.test

@@ -1075,3 +1075,19 @@ s.id_cns = cns.id ORDER BY s.anno_dep DESC LIMIT 1) AS PIPPO FROM
 t2 AS cns;
 
 DROP TABLE t1, t2;
+
+#
+# ref_or_null replacing with ref
+#
+create table t1 (id int not null, text varchar(20) not null default '', primary key (id));
+insert into t1 (id, text) values (1, 'text1'), (2, 'text2'), (3, 'text3'), (4, 'text4'), (5, 'text5'), (6, 'text6'), (7, 'text7'), (8, 'text8'), (9, 'text9'), (10, 'text10'), (11, 'text11'), (12, 'text12');
+select * from t1 where id not in (select id from t1 where id < 8);
+select * from t1 as tt where not exists (select id from t1 where id < 8 and (id = tt.id or id is null) having id is not null);
+explain extended select * from t1 where id not in (select id from t1 where id < 8);
+explain extended select * from t1 as tt where not exists (select id from t1 where id < 8 and (id = tt.id or id is null) having id is not null);
+insert into t1 (id, text) values (1000, 'text1000'), (1001, 'text1001');
+create table t2 (id int not null, text varchar(20) not null default '', primary key (id));
+insert into t2 (id, text) values (1, 'text1'), (2, 'text2'), (3, 'text3'), (4, 'text4'), (5, 'text5'), (6, 'text6'), (7, 'text7'), (8, 'text8'), (9, 'text9'), (10, 'text10'), (11, 'text1'), (12, 'text2'), (13, 'text3'), (14, 'text4'), (15, 'text5'), (16, 'text6'), (17, 'text7'), (18, 'text8'), (19, 'text9'), (20, 'text10'),(21, 'text1'), (22, 'text2'), (23, 'text3'), (24, 'text4'), (25, 'text5'), (26, 'text6'), (27, 'text7'), (28, 'text8'), (29, 'text9'), (30, 'text10'), (31, 'text1'), (32, 'text2'), (33, 'text3'), (34, 'text4'), (35, 'text5'), (36, 'text6'), (37, 'text7'), (38, 'text8'), (39, 'text9'), (40, 'text10'), (41, 'text1'), (42, 'text2'), (43, 'text3'), (44, 'text4'), (45, 'text5'), (46, 'text6'), (47, 'text7'), (48, 'text8'), (49, 'text9'), (50, 'text10');
+select * from t1 a left join t2 b on (a.id=b.id or b.id is null) join t1 c on (if(isnull(b.id), 1000, b.id)=c.id);
+explain extended select * from t1 a left join t2 b on (a.id=b.id or b.id is null) join t1 c on (if(isnull(b.id), 1000, b.id)=c.id);
+drop table t1,t2;

sql/item_subselect.cc

@@ -682,9 +682,9 @@ Item_in_subselect::single_value_transformer(JOIN *join,
     select_lex->ref_pointer_array[0]= select_lex->item_list.head();
     if (select_lex->table_list.elements)
     {
-      Item *having= item, *isnull= item;
+      Item *having= item, *orig_item= item;
       item= func->create(expr, item);
-      if (!abort_on_null)
+      if (!abort_on_null && orig_item->maybe_null)
       {
 	having= new Item_is_not_null_test(this, having);
 	join->having= (join->having ?
@@ -699,7 +699,7 @@ Item_in_subselect::single_value_transformer(JOIN *join,
 	}
 	select_lex->having_fix_field= 0;
 	item= new Item_cond_or(item,
-			       new Item_func_isnull(isnull));
+			       new Item_func_isnull(orig_item));
       }
       item->name= (char *)in_additional_cond;
       join->conds= and_items(join->conds, item);

sql/sql_select.cc

@@ -3240,8 +3240,12 @@ static bool create_ref_for_key(JOIN *join, JOIN_TAB *j, KEYUSE *org_keyuse,
 				  keyuse,join->const_table_map,
 				  &keyinfo->key_part[i],
 				  (char*) key_buff,maybe_null);
-      /* Remmeber if we are going to use REF_OR_NULL */
-      if (keyuse->optimize & KEY_OPTIMIZE_REF_OR_NULL)
+      /*
+	Remmeber if we are going to use REF_OR_NULL
+	But only if field _really_ can be null i.e. we force JT_REF
+	instead of JT_REF_OR_NULL in case if field can't be null
+      */
+      if (keyuse->optimize & KEY_OPTIMIZE_REF_OR_NULL && maybe_null)
 	null_ref_key= key_buff;
       key_buff+=keyinfo->key_part[i].store_length;
     }