SHOW EXPLAIN: Plan returned by SHOW EXPLAIN only contains 'Using temporary' while the standard EXPLAIN says 'Using temporary; Using filesort'

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4112	Using temporary; Using filesort

SELECT a FROM t1 GROUP BY a;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4112	Using temporary

Warnings:

Note	1003	SELECT a FROM t1 GROUP BY a

revision-id: psergey@askmonty.org-20120524182239-gq6jtnnovydnthtl

date: 2012-05-24 22:22:39 +0400

build-date: 2012-05-30 00:21:27 +0400

revno: 3405

CREATE TABLE t1 (a INT);

INSERT INTO t1 VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),

  (10),(11),(12),(13),(14),(15),(16);

INSERT INTO t1 SELECT t11.a FROM t1 t11, t1 t12, t1 t13;

--connect (con1,localhost,root,,)

let $con_id = `SELECT CONNECTION_ID()`;

EXPLAIN SELECT a FROM t1 GROUP BY a;

send SELECT a FROM t1 GROUP BY a;

--connection default

let $run = 20;

while ($run)

{

  --error 0,ER_ERROR_WHEN_EXECUTING_COMMAND

  eval SHOW EXPLAIN FOR $con_id;

  --dec $run

}

--connection con1

--reap