CHEAP SQ: A query with EXISTS subquery, aggregate function in subquery, ORDER BY and LIMIT takes much longer than on main tree if optimizer_prune_level=0

SELECT a FROM t1, t2, t3 AS t3_alias

WHERE b <= ( SELECT SUM(a) FROM t1 )

  AND EXISTS ( SELECT 1 FROM t3 WHERE c > t3_alias.c )

ORDER BY a LIMIT 1;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra

1	PRIMARY	t1	index	NULL	a	5	NULL	40	100.00	Using index; Using temporary; Using filesort

1	PRIMARY	t2	range	b	b	5	NULL	96	100.00	Using where; Using index; Using join buffer (flat, BNL join)

1	PRIMARY	t3_alias	index	NULL	c	5	NULL	40	100.00	Using where; Using index; Using join buffer (incremental, BNL join)

3	DEPENDENT SUBQUERY	t3	index	c	c	5	NULL	40	100.00	Using where; Using index

2	SUBQUERY	t1	index	NULL	a	5	NULL	40	100.00	Using index

Warnings:

Note	1276	Field or reference 'test.t3_alias.c' of SELECT #3 was resolved in SELECT #1

Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` join `test`.`t2` join `test`.`t3` `t3_alias` where ((`test`.`t2`.`b` <= (select sum(`test`.`t1`.`a`) from `test`.`t1`)) and <expr_cache><`test`.`t3_alias`.`c`>(exists(select 1 from `test`.`t3` where (`test`.`t3`.`c` > `test`.`t3_alias`.`c`)))) order by `test`.`t1`.`a` limit 1

id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra

1	PRIMARY	t1	index	NULL	a	5	NULL	40	100.00	Using index; Using temporary; Using filesort

1	PRIMARY	t3_alias	index	NULL	c	5	NULL	40	100.00	Using where; Using index; Using join buffer (flat, BNL join)

1	PRIMARY	t2	index	b	b	5	NULL	100	100.00	Using where; Using index; Using join buffer (incremental, BNL join)

3	DEPENDENT SUBQUERY	t3	index	c	c	5	NULL	40	100.00	Using where; Using index

2	SUBQUERY	t1	index	NULL	a	5	NULL	40	100.00	Using index

Warnings:

Note	1276	Field or reference 'test.t3_alias.c' of SELECT #3 was resolved in SELECT #1

Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` join `test`.`t2` join `test`.`t3` `t3_alias` where ((`test`.`t2`.`b` <= (select sum(`test`.`t1`.`a`) from `test`.`t1`)) and <expr_cache><`test`.`t3_alias`.`c`>(exists(select 1 from `test`.`t3` where (`test`.`t3`.`c` > `test`.`t3_alias`.`c`)))) order by `test`.`t1`.`a` limit 1

SET optimizer_prune_level = 0;

CREATE TABLE t1 (a INT, KEY(a)) ENGINE=MyISAM;

INSERT INTO t1 VALUES

  (0),(8),(1),(8),(9),(24),(6),(1),(6),(2),

  (4),(8),(4),(4),(7),(4),(1),(9),(4),(8);

INSERT INTO t1 SELECT * FROM t1;

CREATE TABLE t2 (b INT, KEY(b)) ENGINE=MyISAM;

INSERT INTO t2 VALUES

  (4),(8),(0),(0),(0),(7),(7),(5),(3),(188),

  (4),(9),(6),(1),(5),(6),(2),(4),(231),(4),

  (3),(3),(7),(6),(7),(9),(4),(4),(2),(1),(2),

  (194),(2),(3),(8),(4),(9),(4),(5),(5),(9),

  (3),(8),(0),(98),(3),(1),(0),(189),(8),(3),

  (3),(9),(6),(8),(3),(9),(5),(9),(2),(2),(5),

  (8),(6),(9),(0),(3),(6),(5),(8),(2),(120),

  (25),(1),(3),(1),(3),(153),(5),(9),(1),(8),

  (7),(6),(2),(4),(7),(3),(8),(4),(6),(1),(7),

  (1),(0),(2),(7),(2),(1),(5);

CREATE TABLE t3 (c INT, KEY(c)) ENGINE=MyISAM;

INSERT INTO t3 VALUES

  (7),(0),(9),(3),(4),(2),(5),(3),(1),(3),(6),

  (7),(5),(1),(204),(224),(9),(5),(0),(3);

INSERT INTO t3 SELECT * FROM t3;

SELECT a FROM t1, t2, t3 AS t3_alias

WHERE b <= ( SELECT SUM(a) FROM t1 )

  AND EXISTS ( SELECT 1 FROM t3 WHERE c > t3_alias.c )

ORDER BY a LIMIT 1;