Extra field 'Using filesort' in EXPLAIN vs 'Using where; Using filesort' in SHOW EXPLAIN on a query with HAVING and ORDER BY

EXPLAIN SELECT alias1.b FROM t1 AS alias1 LEFT JOIN t1 AS alias2 ON (alias2.b = alias1.a)  

WHERE EXISTS ( SELECT * FROM t1 WHERE a <= alias2.a )  

HAVING alias1.b > 10 ORDER BY alias1.b;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	PRIMARY	alias1	ALL	NULL	NULL	NULL	NULL	9	Using filesort

1	PRIMARY	alias2	ref	b	b	5	test.alias1.a	2	Using where

2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	9	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	9	Using where; Using filesort

1	PRIMARY	alias2	ref	b	b	5	test.alias1.a	2	Using where

2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	9	Using where

revision-id: psergey@askmonty.org-20120801115152-qgxtqd0a5vlqrrhx

date: 2012-08-01 15:51:52 +0400

build-date: 2012-08-02 16:12:26 +0300

revno: 3461

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, b INT, KEY(b)) ENGINE=MyISAM;

INSERT INTO t1 VALUES 

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

let $query =

SELECT alias1.b FROM t1 AS alias1 LEFT JOIN t1 AS alias2 ON (alias2.b = alias1.a)  

WHERE EXISTS ( SELECT * FROM t1 WHERE a <= alias2.a )  

HAVING alias1.b > 10 ORDER BY alias1.b;

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;