SHOW EXPLAIN: 'Using where' for a subquery is shown in EXPLAIN, but not in SHOW EXPLAIN output

EXPLAIN SELECT * 

FROM t1 AS alias1, ( SELECT * FROM t2 ) AS alias

WHERE EXISTS ( SELECT * FROM t2 WHERE b = c ) 

OR a <= 10;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	PRIMARY	alias1	ALL	NULL	NULL	NULL	NULL	14	

1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	20	Using join buffer (flat, BNL join)

3	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	20	Using where

#---------------

# SHOW EXPLAIN output:

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	PRIMARY	alias1	ALL	NULL	NULL	NULL	NULL	14	

1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	20	Using join buffer (flat, BNL join)

3	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	20	

revision-id: psergey@askmonty.org-20120727121752-5dmlp1nkhrn01ab5

date: 2012-07-27 16:17:52 +0400

build-date: 2012-08-01 17:33:14 +0300

revno: 3460

index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=off,table_elimination=on,extended_keys=off

CREATE TABLE t1 (a INT) ENGINE=MyISAM;

INSERT INTO t1 VALUES (7),(0),(9),(3),(4),(2),(5),(7),(0),(9),(3),(4),(2),(5);		

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

INSERT INTO t2 VALUES 

(0,4),(8,6),(1,3),(8,5),(9,3),(24,246),(6,2),(1,9),(6,3),(2,8),

(4,1),(8,8),(4,8),(4,5),(7,7),(4,5),(1,1),(9,6),(4,2),(8,9);

let $query =

SELECT * 

FROM t1 AS alias1, ( SELECT * FROM t2 ) AS alias

WHERE EXISTS ( SELECT * FROM t2 WHERE b = c ) 

OR a <= 10;

eval EXPLAIN $query;

--echo #---------------

--echo # SHOW EXPLAIN output:

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

--let $con_id = `SELECT CONNECTION_ID()`

--let $trials = 50

--disable_query_log

while ($trials)

{

  --dec $trials

  --let $run = 1000

  --send_eval $query

  --connection default

  while ($run)

  {

    --error 0,1932

    eval SHOW EXPLAIN FOR $con_id;

    --dec $run

    if (!$mysql_errno)

    {

      --let $run = 0

      --let $trials = 0

      --let $found = 1

    }

  }

  --disable_result_log

  --connection con1

  --reap

  --enable_result_log

}

if (!$found)

{

  --echo ########### Could not catch the query by SHOW EXPLAIN, try again  #############

}

DROP TABLE t1, t2;