SHOW EXPLAIN: select_type returned by SHOW EXPLAIN is different from the normal EXPLAIN (SIMPLE vs PRIMARY)

EXPLAIN SELECT a FROM t1 WHERE ( SELECT SLEEP(0.5) );

id      select_type     table   type    possible_keys   key     key_len ref     rows    Extra

1       PRIMARY t1      ALL     NULL    NULL    NULL    NULL    2       Using where

Warnings:

Note    1249    Select 2 was reduced during optimization

SELECT a FROM t1 WHERE ( SELECT SLEEP(0.5) );

SHOW EXPLAIN FOR 2;

id      select_type     table   type    possible_keys   key     key_len ref     rows    Extra

1       SIMPLE  t1      ALL     NULL    NULL    NULL    NULL    2       Using where

Warnings:

Note    1003    SELECT a FROM t1 WHERE ( SELECT SLEEP(0.5) )

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

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

revno: 3405

CREATE TABLE t1 (a INT);

INSERT INTO t1 VALUES (1),(2);

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

let $con_id = `SELECT CONNECTION_ID()`;

EXPLAIN SELECT a FROM t1 WHERE ( SELECT SLEEP(0.5) );

send SELECT a FROM t1 WHERE ( SELECT SLEEP(0.5) );

--connection default

let $run = 100;

while ($run)

{

  --error 0,ER_ERROR_WHEN_EXECUTING_COMMAND

  --eval SHOW EXPLAIN FOR $con_id

  --dec $run

  if (!$mysql_errno)

  {

    let $run = 0;

  }

}

--connection con1

--reap