2001-09-27 23:05:54 -06:00
drop table if exists t1;
create table t1 (id int not null, str char(10), unique(str));
2003-01-20 18:17:14 +02:00
explain select * from t1;
2003-01-21 21:07:59 +02:00
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 system NULL NULL NULL NULL 0 const row not found
2001-09-27 23:05:54 -06:00
insert into t1 values (1, null),(2, null),(3, "foo"),(4, "bar");
select * from t1 where str is null;
2000-12-28 03:56:38 +02:00
id str
1 NULL
2 NULL
2001-09-27 23:05:54 -06:00
select * from t1 where str="foo";
2000-12-28 03:56:38 +02:00
id str
3 foo
2001-09-27 23:05:54 -06:00
explain select * from t1 where str is null;
2002-09-26 23:08:22 +03:00
id select_type table type possible_keys key key_len ref rows Extra
2009-12-15 10:16:46 +03:00
1 SIMPLE t1 ref str str 11 const 1 Using index condition
2001-09-27 23:05:54 -06:00
explain select * from t1 where str="foo";
2002-09-26 23:08:22 +03:00
id select_type table type possible_keys key key_len ref rows Extra
2002-10-03 18:47:04 +03:00
1 SIMPLE t1 const str str 11 const 1
2001-09-27 23:05:54 -06:00
explain select * from t1 ignore key (str) where str="foo";
2002-09-26 23:08:22 +03:00
id select_type table type possible_keys key key_len ref rows Extra
2002-11-21 15:56:48 +02:00
1 SIMPLE t1 ALL NULL NULL NULL NULL 4 Using where
2001-09-27 23:05:54 -06:00
explain select * from t1 use key (str,str) where str="foo";
2002-09-26 23:08:22 +03:00
id select_type table type possible_keys key key_len ref rows Extra
2002-10-03 18:47:04 +03:00
1 SIMPLE t1 const str str 11 const 1
2001-09-27 23:05:54 -06:00
explain select * from t1 use key (str,str,foo) where str="foo";
2006-06-06 20:21:36 +03:00
ERROR 42000: Key 'foo' doesn't exist in table 't1'
2001-09-27 23:05:54 -06:00
explain select * from t1 ignore key (str,str,foo) where str="foo";
2006-06-06 20:21:36 +03:00
ERROR 42000: Key 'foo' doesn't exist in table 't1'
2001-09-27 23:05:54 -06:00
drop table t1;
explain select 1;
2002-09-26 23:08:22 +03:00
id select_type table type possible_keys key key_len ref rows Extra
2002-12-14 17:43:01 +02:00
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL No tables used
2003-02-07 17:57:07 +02:00
create table t1 (a int not null);
explain select count(*) from t1;
2003-02-08 02:09:21 +02:00
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
2003-02-07 17:57:07 +02:00
insert into t1 values(1);
explain select count(*) from t1;
2003-02-08 02:09:21 +02:00
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
2003-02-07 17:57:07 +02:00
insert into t1 values(1);
explain select count(*) from t1;
2003-02-08 02:09:21 +02:00
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
2003-02-07 17:57:07 +02:00
drop table t1;
2004-05-14 13:08:22 +05:00
set names koi8r;
create table <20> <> <EFBFBD> (<28> <> <EFBFBD> 0 int, <20> <> <EFBFBD> 1 int, key <20> <> <EFBFBD> 0 (<28> <> <EFBFBD> 0), key <20> <> <EFBFBD> 01 (<28> <> <EFBFBD> 0,<2C> <> <EFBFBD> 1));
insert into <20> <> <EFBFBD> (<28> <> <EFBFBD> 0) values (1);
insert into <20> <> <EFBFBD> (<28> <> <EFBFBD> 0) values (2);
explain select <20> <> <EFBFBD> 0 from <20> <> <EFBFBD> where <20> <> <EFBFBD> 0=1;
id select_type table type possible_keys key key_len ref rows Extra
2009-12-15 10:16:46 +03:00
1 SIMPLE <09> <> <EFBFBD> ref <09> <> <EFBFBD> 0,<2C> <> <EFBFBD> 01 <09> <> <EFBFBD> 0 5 const 1 Using index
2004-05-14 13:08:22 +05:00
drop table <20> <> <EFBFBD> ;
set names latin1;
2006-05-03 18:02:43 +04:00
select 3 into @v1;
explain select 3 into @v1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL No tables used
2007-03-07 21:44:58 +03:00
create table t1(f1 int, f2 int);
insert into t1 values (1,1);
create view v1 as select * from t1 where f1=1;
explain extended select * from v1 where f2=1;
2007-03-08 20:57:12 +04:00
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 system NULL NULL NULL NULL 1 100.00
2007-03-07 21:44:58 +03:00
Warnings:
2007-03-10 00:29:02 +03:00
Note 1003 select '1' AS `f1`,'1' AS `f2` from `test`.`t1` where 1
2007-03-07 21:44:58 +03:00
explain extended select * from t1 where 0;
2007-03-08 20:57:12 +04:00
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
2007-03-07 21:44:58 +03:00
Warnings:
Note 1003 select `test`.`t1`.`f1` AS `f1`,`test`.`t1`.`f2` AS `f2` from `test`.`t1` where 0
explain extended select * from t1 where 1;
2007-03-08 20:57:12 +04:00
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 system NULL NULL NULL NULL 1 100.00
2007-03-07 21:44:58 +03:00
Warnings:
2007-03-10 00:29:02 +03:00
Note 1003 select '1' AS `f1`,'1' AS `f2` from `test`.`t1` where 1
2007-03-07 21:44:58 +03:00
explain extended select * from t1 having 0;
2007-03-08 20:57:12 +04:00
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL NULL Impossible HAVING
2007-03-07 21:44:58 +03:00
Warnings:
Note 1003 select `test`.`t1`.`f1` AS `f1`,`test`.`t1`.`f2` AS `f2` from `test`.`t1` having 0
explain extended select * from t1 having 1;
2007-03-08 20:57:12 +04:00
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 system NULL NULL NULL NULL 1 100.00
2007-03-07 21:44:58 +03:00
Warnings:
2007-03-10 00:29:02 +03:00
Note 1003 select '1' AS `f1`,'1' AS `f2` from `test`.`t1` having 1
2007-03-08 00:27:42 +03:00
drop view v1;
2007-03-07 21:44:58 +03:00
drop table t1;
2007-11-16 13:58:09 +03:00
CREATE TABLE t1(c INT);
INSERT INTO t1 VALUES (),();
CREATE TABLE t2 (b INT,
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b),
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b),
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b),
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b),
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b),
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b),
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b),
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b));
INSERT INTO t2 VALUES (),(),();
EXPLAIN SELECT 1 FROM
(SELECT 1 FROM t2,t1 WHERE b < c GROUP BY 1 LIMIT 1) AS d2;
id select_type table type possible_keys key key_len ref rows Extra
X X X X X X X X X const row not found
X X X X X X X X X
X X X X X X X X X Range checked for each record (index map: 0xFFFFFFFFFF)
DROP TABLE t2;
DROP TABLE t1;
2008-10-06 17:17:25 +03:00
CREATE TABLE t1(a INT);
CREATE TABLE t2(a INT);
INSERT INTO t1 VALUES (1),(2);
INSERT INTO t2 VALUES (1),(2);
EXPLAIN EXTENDED SELECT 1
FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00
2 DERIVED t1 ALL NULL NULL NULL NULL 2 100.00 Using temporary; Using filesort
2010-10-18 13:33:05 -07:00
2 DERIVED t2 ALL NULL NULL NULL NULL 2 100.00 Using join buffer (flat, BNL join)
2008-10-06 17:17:25 +03:00
Warnings:
Note 1003 select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
EXPLAIN EXTENDED SELECT 1
FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00
2 DERIVED t1 ALL NULL NULL NULL NULL 2 100.00 Using temporary; Using filesort
2010-10-18 13:33:05 -07:00
2 DERIVED t2 ALL NULL NULL NULL NULL 2 100.00 Using join buffer (flat, BNL join)
2008-10-06 17:17:25 +03:00
Warnings:
Note 1003 select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
prepare s1 from
'EXPLAIN EXTENDED SELECT 1
FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1';
execute s1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00
2 DERIVED t1 ALL NULL NULL NULL NULL 2 100.00 Using temporary; Using filesort
2010-10-18 13:33:05 -07:00
2 DERIVED t2 ALL NULL NULL NULL NULL 2 100.00 Using join buffer (flat, BNL join)
2008-10-06 17:17:25 +03:00
Warnings:
Note 1003 select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
prepare s1 from
'EXPLAIN EXTENDED SELECT 1
FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1';
execute s1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00
2 DERIVED t1 ALL NULL NULL NULL NULL 2 100.00 Using temporary; Using filesort
2010-10-18 13:33:05 -07:00
2 DERIVED t2 ALL NULL NULL NULL NULL 2 100.00 Using join buffer (flat, BNL join)
2008-10-06 17:17:25 +03:00
Warnings:
Note 1003 select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
execute s1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00
2 DERIVED t1 ALL NULL NULL NULL NULL 2 100.00 Using temporary; Using filesort
2010-10-18 13:33:05 -07:00
2 DERIVED t2 ALL NULL NULL NULL NULL 2 100.00 Using join buffer (flat, BNL join)
2008-10-06 17:17:25 +03:00
Warnings:
Note 1003 select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
DROP TABLE t1,t2;
2009-03-11 14:10:44 +02:00
CREATE TABLE t1 (a INT PRIMARY KEY);
EXPLAIN EXTENDED SELECT COUNT(a) FROM t1 USE KEY(a);
2009-03-11 14:29:59 +02:00
ERROR 42000: Key 'a' doesn't exist in table 't1'
2009-03-11 14:10:44 +02:00
DROP TABLE t1;
2009-09-04 12:20:53 +05:00
CREATE TABLE t1(a LONGTEXT);
INSERT INTO t1 VALUES (repeat('a',@@global.max_allowed_packet));
INSERT INTO t1 VALUES (repeat('b',@@global.max_allowed_packet));
EXPLAIN SELECT DISTINCT 1 FROM t1,
(SELECT DISTINCTROW a AS away FROM t1 GROUP BY a WITH ROLLUP) as d1
WHERE t1.a = d1.a;
ERROR 42S22: Unknown column 'd1.a' in 'where clause'
DROP TABLE t1;
2008-10-27 12:26:32 +03:00
#
2010-03-02 18:00:53 +00:00
# Bug#48295:
# explain extended crash with subquery and ONLY_FULL_GROUP_BY sql_mode
#
CREATE TABLE t1 (f1 INT);
SELECT @@session.sql_mode INTO @old_sql_mode;
SET SESSION sql_mode='ONLY_FULL_GROUP_BY';
EXPLAIN EXTENDED SELECT 1 FROM t1
WHERE f1 > ALL( SELECT t.f1 FROM t1,t1 AS t );
ERROR 42000: Mixing of GROUP columns (MIN(),MAX(),COUNT(),...) with no GROUP columns is illegal if there is no GROUP BY clause
SHOW WARNINGS;
Level Code Message
Error 1140 Mixing of GROUP columns (MIN(),MAX(),COUNT(),...) with no GROUP columns is illegal if there is no GROUP BY clause
Note 1003 select 1 AS `1` from `test`.`t1` where <not>(<exists>(...))
SET SESSION sql_mode=@old_sql_mode;
DROP TABLE t1;
End of 5.0 tests.
2010-03-02 18:13:43 +00:00
#
2008-10-27 12:26:32 +03:00
# Bug#37870: Usage of uninitialized value caused failed assertion.
#
2008-11-05 18:40:23 +03:00
create table t1 (dt datetime not null, t time not null);
2008-10-27 12:26:32 +03:00
create table t2 (dt datetime not null);
2008-11-05 18:40:23 +03:00
insert into t1 values ('2001-01-01 1:1:1', '1:1:1'),
('2001-01-01 1:1:1', '1:1:1');
2008-10-27 12:26:32 +03:00
insert into t2 values ('2001-01-01 1:1:1'), ('2001-01-01 1:1:1');
flush tables;
EXPLAIN SELECT OUTR.dt FROM t1 AS OUTR WHERE OUTR.dt IN (SELECT INNR.dt FROM t2 AS INNR WHERE OUTR.dt IS NULL );
id select_type table type possible_keys key key_len ref rows Extra
2010-11-03 12:26:18 -07:00
1 PRIMARY OUTR ALL NULL NULL NULL NULL 2 Using where; Start temporary
1 PRIMARY INNR ALL NULL NULL NULL NULL 2 Using where; End temporary; Using join buffer (flat, BNL join)
2008-11-05 18:40:23 +03:00
flush tables;
2008-10-27 12:26:32 +03:00
SELECT OUTR.dt FROM t1 AS OUTR WHERE OUTR.dt IN (SELECT INNR.dt FROM t2 AS INNR WHERE OUTR.dt IS NULL );
dt
2008-11-05 18:40:23 +03:00
flush tables;
EXPLAIN SELECT OUTR.dt FROM t1 AS OUTR WHERE OUTR.dt IN ( SELECT INNR.dt FROM t2 AS INNR WHERE OUTR.t < '2005-11-13 7:41:31' );
id select_type table type possible_keys key key_len ref rows Extra
2010-11-03 12:26:18 -07:00
1 PRIMARY OUTR ALL NULL NULL NULL NULL 2 Using where; Start temporary
1 PRIMARY INNR ALL NULL NULL NULL NULL 2 Using where; End temporary; Using join buffer (flat, BNL join)
2008-11-05 18:40:23 +03:00
flush tables;
SELECT OUTR.dt FROM t1 AS OUTR WHERE OUTR.dt IN ( SELECT INNR.dt FROM t2 AS INNR WHERE OUTR.t < '2005-11-13 7:41:31' );
dt
2001-01-01 01:01:01
2001-01-01 01:01:01
2008-10-27 12:26:32 +03:00
drop tables t1, t2;
2009-10-29 16:01:54 -07:00
#
2010-02-26 17:40:01 +04:00
# Bug#47669: Query showed by EXPLAIN EXTENDED gives different result from original query
2009-10-29 16:01:54 -07:00
#
2010-02-26 17:40:01 +04:00
CREATE TABLE t1 (c int);
INSERT INTO t1 VALUES (NULL);
CREATE TABLE t2 (d int);
INSERT INTO t2 VALUES (NULL), (0);
EXPLAIN EXTENDED SELECT (SELECT 1 FROM t2 WHERE d = c) FROM t1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t1 system NULL NULL NULL NULL 1 100.00
2 DEPENDENT SUBQUERY t2 ALL NULL NULL NULL NULL 2 100.00 Using where
Warnings:
Note 1276 Field or reference 'test.t1.c' of SELECT #2 was resolved in SELECT #1
2010-09-06 15:34:24 +03:00
Note 1003 select <expr_cache><NULL>((select 1 from `test`.`t2` where (`test`.`t2`.`d` = NULL))) AS `(SELECT 1 FROM t2 WHERE d = c)` from `test`.`t1`
2010-02-26 17:40:01 +04:00
DROP TABLE t1, t2;
2010-04-30 15:10:48 +04:00
#
# Bug #48419: another explain crash..
#
CREATE TABLE t1 (a INT);
CREATE TABLE t2 (b BLOB, KEY b(b(100)));
INSERT INTO t2 VALUES ('1'), ('2'), ('3');
FLUSH TABLES;
EXPLAIN SELECT 1 FROM t1 WHERE a = (SELECT 1 FROM t1 t JOIN t2 WHERE b <= 1 AND t.a);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
DROP TABLE t1, t2;
2010-05-29 22:16:45 +04:00
#
# Bug #48573: difference of index selection between rpm binary and
# .tar.gz, windows vs linux..
#
CREATE TABLE t1(c1 INT, c2 INT, c4 INT, c5 INT, KEY(c2, c5), KEY(c2, c4, c5));
INSERT INTO t1 VALUES(4, 1, 1, 1);
INSERT INTO t1 VALUES(3, 1, 1, 1);
INSERT INTO t1 VALUES(2, 1, 1, 1);
INSERT INTO t1 VALUES(1, 1, 1, 1);
EXPLAIN SELECT c1 FROM t1 WHERE c2 = 1 AND c4 = 1 AND c5 = 1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref c2,c2_2 c2 10 const,const 3 Using where
DROP TABLE t1;
2010-10-18 16:12:27 +04:00
#
# Bug#56814 Explain + subselect + fulltext crashes server
#
CREATE TABLE t1(f1 VARCHAR(6) NOT NULL,
FULLTEXT KEY(f1),UNIQUE(f1));
INSERT INTO t1 VALUES ('test');
EXPLAIN SELECT 1 FROM t1
WHERE 1 > ALL((SELECT 1 FROM t1 JOIN t1 a ON (MATCH(t1.f1) AGAINST (""))
WHERE t1.f1 GROUP BY t1.f1));
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 system NULL NULL NULL NULL 1
Fix LP BUG#715069
Analysis:
The wrong result is a consquence of sorting the subquery
result and then selecting only the first row due to the
artificial LIMIT 1 introduced by the fix_fields phase.
Normally, if there is an ORDER BY in a subquery, the ORDER
is removed (Item_in_subselect::select_in_like_transformer),
however if a GROUP BY is transformed into ORDER, this happens
later, after the removal of the ORDER clause of subqueries, so
we end up with a subquery with an ORDER clause, and an artificially
added LIMIT 1.
The reason why the same works in the main 5.3 without MWL#89, is
that the 5.3 performs all subquery transformations, including
IN->EXISTS before JOIN::optimize(). The beginning of JOIN::optimize
does:
if (having || (select_options & OPTION_FOUND_ROWS))
select_limit= HA_POS_ERROR;
which sets the limit back to infinity, thus 5.3 sorts the whole
subquery result, and IN performs the lookup into all subquery result
rows.
Solution:
Sorting of subqueries without LIMIT is meaningless. Since LIMIT in
subqueries is not supported, the patch removes sorting by setting
join->skip_sort_order= true
for each subquery JOIN object. This improves a number of execution
plans to not perform unnecessary sorting at all.
2011-04-20 18:36:55 +03:00
2 SUBQUERY a system NULL NULL NULL NULL 1
2010-10-18 16:12:27 +04:00
2 SUBQUERY t1 fulltext f1 f1 0 1 Using where
PREPARE stmt FROM
'EXPLAIN SELECT 1 FROM t1
WHERE 1 > ALL((SELECT 1 FROM t1 RIGHT OUTER JOIN t1 a
ON (MATCH(t1.f1) AGAINST (""))
WHERE t1.f1 GROUP BY t1.f1))';
EXECUTE stmt;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 system NULL NULL NULL NULL 1
2 SUBQUERY a system NULL NULL NULL NULL 1 Using filesort
2 SUBQUERY t1 fulltext f1 f1 0 1 Using where
EXECUTE stmt;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 system NULL NULL NULL NULL 1
2 SUBQUERY a system NULL NULL NULL NULL 1 Using filesort
2 SUBQUERY t1 fulltext f1 f1 0 1 Using where
DEALLOCATE PREPARE stmt;
PREPARE stmt FROM
'EXPLAIN SELECT 1 FROM t1
WHERE 1 > ALL((SELECT 1 FROM t1 JOIN t1 a
ON (MATCH(t1.f1) AGAINST (""))
WHERE t1.f1 GROUP BY t1.f1))';
EXECUTE stmt;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 system NULL NULL NULL NULL 1
2 SUBQUERY a system NULL NULL NULL NULL 1 Using filesort
2 SUBQUERY t1 fulltext f1 f1 0 1 Using where
EXECUTE stmt;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 system NULL NULL NULL NULL 1
2 SUBQUERY a system NULL NULL NULL NULL 1 Using filesort
2 SUBQUERY t1 fulltext f1 f1 0 1 Using where
DEALLOCATE PREPARE stmt;
DROP TABLE t1;
2009-03-11 14:29:59 +02:00
End of 5.1 tests.
2011-05-04 18:08:44 -07:00
#
# Bug#776295: EXPLAIN EXTENDED with always false multiple equality
# in the WHERE condition of a derived table
#
CREATE TABLE t1 (a int) ;
CREATE TABLE t2 (a int) ;
INSERT INTO t2 VALUES (8);
EXPLAIN EXTENDED
SELECT * FROM ( SELECT t1.a FROM t1,t2 WHERE t2.a = t1.a ) AS t;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY <derived2> system NULL NULL NULL NULL 0 0.00 const row not found
2 DERIVED NULL NULL NULL NULL NULL NULL NULL NULL no matching row in const table
Warnings:
Note 1003 select NULL AS `a` from (select NULL AS `a` from `test`.`t1` join `test`.`t2` where 0) `t`
DROP TABLE t1,t2;