MDEV-21614 Wrong query results with optimizer_switch="split_materiali…

…zed=on" Do not materialize a semi-join nest if it contains a materialized derived table /view that potentially can be subject to the split optimization. Splitting of materialization of such nest would help, but currently there is no code to support this technique.
MariaDB · Feb 8, 2020 · 8d7462e · 8d7462e
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diff --git a/mysql-test/main/derived_cond_pushdown.result b/mysql-test/main/derived_cond_pushdown.result
@@ -16829,4 +16829,93 @@ id	username	id	userid	logindate
 2	user2	3	2	2017-06-19 12:17:02
 set join_cache_level=default;
 DROP TABLE t1,t2;
+#
+# MDEV-21614: potentially splittable materialized derived/view
+#             within materialized semi-join
+#
+create table t1 (
+id int not null auto_increment primary key,
+a int not null
+) engine=myisam;
+create table t2 (
+id int not null auto_increment primary key,
+ro_id int not null,
+flag int not null, key (ro_id)
+) engine=myisam;
+insert into t1(a) select seq+100 from seq_1_to_20;
+insert into t2(ro_id,flag) select seq, 1 from seq_1_to_20;
+insert into t2(ro_id,flag) select seq, 0 from seq_1_to_20;
+create view v1 as
+select t1.* from t1 left join t2 on (t1.id = t2.ro_id AND t2.flag = 1)
+group by t1.id;
+select id, a from t1 where  id in (select id from v1);
+id	a
+1	101
+2	102
+3	103
+4	104
+5	105
+6	106
+7	107
+8	108
+9	109
+10	110
+11	111
+12	112
+13	113
+14	114
+15	115
+16	116
+17	117
+18	118
+19	119
+20	120
+explain extended select id, a from t1 where  id in (select id from v1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	ALL	PRIMARY	NULL	NULL	NULL	20	100.00	
+1	PRIMARY	<derived3>	ref	key0	key0	4	test.t1.id	2	100.00	FirstMatch(t1)
+3	LATERAL DERIVED	t1	eq_ref	PRIMARY	PRIMARY	4	test.t1.id	1	100.00	
+3	LATERAL DERIVED	t2	ref	ro_id	ro_id	4	test.t1.id	1	100.00	Using where
+Warnings:
+Note	1003	/* select#1 */ select `test`.`t1`.`id` AS `id`,`test`.`t1`.`a` AS `a` from `test`.`t1` semi join (`test`.`v1`) where `v1`.`id` = `test`.`t1`.`id`
+select id, a from t1
+where id in (select id
+from (select t1.* from t1 left join t2
+on (t1.id = t2.ro_id AND t2.flag = 1)
+group by t1.id) dt);
+id	a
+1	101
+2	102
+3	103
+4	104
+5	105
+6	106
+7	107
+8	108
+9	109
+10	110
+11	111
+12	112
+13	113
+14	114
+15	115
+16	116
+17	117
+18	118
+19	119
+20	120
+explain extended select id, a from t1
+where id in (select id
+from (select t1.* from t1 left join t2
+on (t1.id = t2.ro_id AND t2.flag = 1)
+group by t1.id) dt);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	ALL	PRIMARY	NULL	NULL	NULL	20	100.00	
+1	PRIMARY	<derived3>	ref	key0	key0	4	test.t1.id	2	100.00	FirstMatch(t1)
+3	LATERAL DERIVED	t1	eq_ref	PRIMARY	PRIMARY	4	test.t1.id	1	100.00	
+3	LATERAL DERIVED	t2	ref	ro_id	ro_id	4	test.t1.id	1	100.00	Using where
+Warnings:
+Note	1003	/* select#1 */ select `test`.`t1`.`id` AS `id`,`test`.`t1`.`a` AS `a` from `test`.`t1` semi join ((/* select#3 */ select `test`.`t1`.`id` AS `id`,`test`.`t1`.`a` AS `a` from `test`.`t1` left join `test`.`t2` on(`test`.`t2`.`ro_id` = `test`.`t1`.`id` and `test`.`t2`.`flag` = 1) where `test`.`t1`.`id` = `test`.`t1`.`id` group by `test`.`t1`.`id`) `dt`) where `dt`.`id` = `test`.`t1`.`id`
+drop view v1;
+drop table t1,t2;
 # End of 10.3 tests
diff --git a/mysql-test/main/derived_cond_pushdown.test b/mysql-test/main/derived_cond_pushdown.test
@@ -1,3 +1,4 @@
+--source include/have_sequence.inc
 --source include/default_optimizer_switch.inc
 let $no_pushdown= set statement optimizer_switch='condition_pushdown_for_derived=off' for;
 set @@join_buffer_size=256*1024;
@@ -3328,4 +3329,46 @@ set join_cache_level=default;
 
 DROP TABLE t1,t2;
 
+
+--echo #
+--echo # MDEV-21614: potentially splittable materialized derived/view
+--echo #             within materialized semi-join
+--echo #
+
+create table t1 (
+  id int not null auto_increment primary key,
+  a int not null
+) engine=myisam;
+
+create table t2 (
+  id int not null auto_increment primary key,
+  ro_id int not null,
+  flag int not null, key (ro_id)
+) engine=myisam;
+
+insert into t1(a) select seq+100 from seq_1_to_20;
+insert into t2(ro_id,flag) select seq, 1 from seq_1_to_20;
+insert into t2(ro_id,flag) select seq, 0 from seq_1_to_20;
+
+create view v1 as
+select t1.* from t1 left join t2 on (t1.id = t2.ro_id AND t2.flag = 1)
+  group by t1.id;
+
+let $q1=
+select id, a from t1 where  id in (select id from v1);
+eval $q1;
+eval explain extended $q1;
+
+let $q2=
+select id, a from t1
+  where id in (select id
+               from (select t1.* from t1 left join t2
+                                      on (t1.id = t2.ro_id AND t2.flag = 1)
+                     group by t1.id) dt);
+eval $q2;
+eval explain extended $q2;
+
+drop view v1;
+drop table t1,t2;
+
 --echo # End of 10.3 tests
diff --git a/sql/opt_split.cc b/sql/opt_split.cc
@@ -307,7 +307,7 @@ struct SplM_field_ext_info: public SplM_field_info
     8. P contains some references on the columns of the joined tables C
        occurred also in the select list of this join
     9. There are defined some keys usable for ref access of fields from C
-       with available statistics. 
+       with available statistics.
 
   @retval
     true   if the answer is positive
@@ -477,6 +477,15 @@ bool JOIN::check_for_splittable_materialized()
   /* Attach this info to the table T */
   derived->table->set_spl_opt_info(spl_opt_info);
 
+  /*
+    If this is specification of a materialized derived table T that is
+    potentially splittable and is used in the from list of the right operand
+    of an IN predicand transformed to a semi-join then the embedding semi-join
+    nest is not allowed to be materialized.
+  */
+  if (derived && derived->is_materialized_derived() &&
+      derived->embedding && derived->embedding->sj_subq_pred)
+    derived->embedding->sj_subq_pred->types_allow_materialization= FALSE;
   return true;
 }