id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	<derived2>	system					0	const row not found
1	PRIMARY	clients	ALL					1	Using temporary; Using filesort
1	PRIMARY	<derived3>	ALL					1	(null)
3	DERIVED	messages	ALL					31	Using where; Using temporary; Using filesort
2	DERIVED	messages	ALL					31	Using where; Using temporary; Using filesort

---------

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	clients	index		PRIMARY	4		1	Using temporary; Using filesort
3	DEPENDENT SUBQUERY	mes_open	ALL					31	Using where
2	DEPENDENT SUBQUERY	mes_new	ALL					31	Using where