Derived table merge optimization does not work for delete and update

--source include/have_sequence.inc

create table t1 (a int, b int); insert into t1 select seq, seq from seq_1_to_10;

create table t2 (a int, b int); insert into t2 select seq, seq from seq_1_to_10;

create table t3 (a int, b int); insert into t3 select seq, seq from seq_1_to_10;

explain delete t1.* from t1, (select t2.b as b1, t3.b as b2 from t2, t3 where t3.a=t2.a) DT where t1.b=DT.b1  and b2<1;

set optimizer_switch='derived_with_keys=off';

explain select * from t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a) DT where t1.b+1=1+DT.b1;

explain delete t1.* from t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a) DT where t1.b+1=1+DT.b1;

create view DT as select t2.b as b1 from t2, t3 where t3.a=t2.a;

explain delete t1.* from t1, DT where t1.b+1=1+DT.b1;

drop view DT;

drop table t1,t2,t3;

explain delete t1.* from t1, (select t2.b as b1, t3.b as b2 from t2, t3 where t3.a=t2.a) DT where t1.b=DT.b1  and b2<1;

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>	ref	key0	key0	5	test.t1.b	10	Using where

2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	10	

2	DERIVED	t3	ALL	NULL	NULL	NULL	NULL	10	Using where; Using join buffer (flat, BNL join)

explain select * from t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a) DT where t1.b+1=1+DT.b1;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	

1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	10	Using where; Using join buffer (flat, BNL join)

1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	10	Using where; Using join buffer (incremental, BNL join)

explain delete t1.* from t1, (select t2.b as b1 from t2, t3 where t3.a=t2.a) DT where t1.b+1=1+DT.b1;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	10	

1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	100	Using where

2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	10	

2	DERIVED	t3	ALL	NULL	NULL	NULL	NULL	10	Using where; Using join buffer (flat, BNL join)

explain delete t1.* from t1, DT where t1.b+1=1+DT.b1;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	

1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	10	Using where

1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	10	Using where

bool forced_no_merge_for_update_delete=

           belong_to_view ? belong_to_view->updating :

                           !unit->outer_select()->outer_select();

(gdb) print forced_no_merge_for_update_delete

  $28 = true