MDEV-17382 Hash join algorithm should not be used to join materialized

 derived table / view by equality Now rows of a materialized derived table are always put into a temporary table before join operation. If BNLH is used to join this table with the result of a partial join then both operands of the join are actually put into main memory. In most cases this is not efficient. We could avoid this by sending the rows of the derived table directly to the join operation. However this kind of data flow is not supported yet. Fixed by not allowing usage of hash join algorithm to join a materialized derived table if it's joined by an equality predicate of the form f=e where f is a field of the derived table.

Author: igorbabaev

mysql-test/r/derived_opt.result

@@ -499,9 +499,42 @@ where
 D1.a= t1.a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	10	Using where
-1	PRIMARY	<derived2>hash_ALLkey0#hash#key0	5	test.t1.a100	Using join buffer (flat, BNLH join)
+1	PRIMARY	<derived2>refkey0	key0	5	test.t1.a10
 2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	100	Using filesort
 set join_cache_level=@tmp_jcl;
 set optimizer_switch=@tmp_os;
 drop table t1, t2;
+#
+# Bug mdev-17382: equi-join of derived table with join_cache_level=4
+#
+CREATE TABLE t1 (
+id int NOT NULL,
+amount decimal DEFAULT NULL,
+PRIMARY KEY (id)
+);
+CREATE TABLE t2 (
+id int NOT NULL,
+name varchar(50) DEFAULT NULL,
+PRIMARY KEY (id)
+);
+INSERT INTO t1 VALUES
+(1, 10.0000), (2, 20.0000), (3, 30.0000), (4, 40.0000),
+(5, NULL), (6, NULL), (7, 70.0000), (8, 80.0000);
+INSERT INTO t2 VALUES
+(1,'A'), (2,'B'), (3,'C'), (4,'D'), (5, NULL), (6, NULL),
+(7,'E'), (8,'F'), (9,'G'), (10,'H'), (11, NULL), (12, NULL);
+set join_cache_level=4;
+EXPLAIN
+SELECT t2.id,t2.name,t.total_amt
+FROM t2
+LEFT JOIN
+(SELECT id, sum(amount) total_amt FROM t1 GROUP BY id) AS t
+ON t2.id=t.id
+WHERE t2.id < 3;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t2	range	PRIMARY	PRIMARY	4	NULL	3	Using index condition
+1	PRIMARY	<derived2>	ref	key0	key0	5	test.t2.id	2
+2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	8	Using temporary; Using filesort
+set join_cache_level=default;
+DROP TABLE t1,t2;
 set optimizer_switch=@exit_optimizer_switch;

mysql-test/r/innodb_mrr_cpk.result

@@ -226,7 +226,7 @@ set join_cache_level=3;
 explain SELECT 1 FROM (SELECT url, id FROM t2 LIMIT 1 OFFSET 20) derived RIGHT JOIN t1 ON t1.id = derived.id;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	#
-1	PRIMARY	<derived2>hash_ALLkey0#hash#key0	25	test.t1.id	#Using join buffer (flat, BNLH join)
+1	PRIMARY	<derived2>refkey0	key0	25	test.t1.id	#
 2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	#
 set join_cache_level= @tmp_mdev5037;
 drop table t0,t1,t2;

mysql-test/t/derived_opt.test

@@ -363,5 +363,43 @@ set join_cache_level=@tmp_jcl;
 set optimizer_switch=@tmp_os;
 drop table t1, t2;
 
+--echo #
+--echo # Bug mdev-17382: equi-join of derived table with join_cache_level=4
+--echo #
+
+CREATE TABLE t1 (
+ id int NOT NULL,
+ amount decimal DEFAULT NULL,
+PRIMARY KEY (id)
+);
+
+CREATE TABLE t2 (
+ id int NOT NULL,
+ name varchar(50) DEFAULT NULL,
+PRIMARY KEY (id)
+);
+
+INSERT INTO t1 VALUES
+(1, 10.0000), (2, 20.0000), (3, 30.0000), (4, 40.0000),
+(5, NULL), (6, NULL), (7, 70.0000), (8, 80.0000);
+
+INSERT INTO t2 VALUES
+(1,'A'), (2,'B'), (3,'C'), (4,'D'), (5, NULL), (6, NULL),
+(7,'E'), (8,'F'), (9,'G'), (10,'H'), (11, NULL), (12, NULL);
+
+set join_cache_level=4;
+
+EXPLAIN
+SELECT t2.id,t2.name,t.total_amt
+ FROM t2
+ LEFT JOIN
+ (SELECT id, sum(amount) total_amt FROM t1 GROUP BY id) AS t
+ ON t2.id=t.id
+ WHERE t2.id < 3;
+
+set join_cache_level=default;
+
+DROP TABLE t1,t2;
+
 # The following command must be the last one the file 
 set optimizer_switch=@exit_optimizer_switch;

sql/sql_select.cc

@@ -10054,7 +10054,15 @@ uint check_join_cache_usage(JOIN_TAB *tab,
  effort now.
  */
  if (tab->table->pos_in_table_list->is_materialized_derived())
+ {
  no_bka_cache= true;
+ /*
+ Don't use hash join algorithm if the temporary table for the rows
+ of the derived table will be created with an equi-join key.
+ */
+ if (tab->table->s->keys)
+ no_hashed_cache= true;
+ }
 
  /*
  Don't use join buffering if we're dictated not to by no_jbuf_after