select (select 2);
(select 2)
2
SELECT (SELECT 1) UNION SELECT (SELECT 2);
(SELECT 1)
1
2
SELECT (SELECT (SELECT 0 UNION SELECT 0));
(SELECT (SELECT 0 UNION SELECT 0))
0
SELECT (SELECT 1 FROM (SELECT 1) HAVING a=1) as a;
Reference 'a' not supported (forward reference in item list)
SELECT (SELECT 1 FROM (SELECT 1) HAVING b=1) as a,(SELECT 1 FROM (SELECT 1) HAVING a=1) as b;
Reference 'b' not supported (forward reference in item list)
SELECT (SELECT 1),MAX(1) FROM (SELECT 1);
(SELECT 1)	MAX(1)
1	1
SELECT (SELECT a) as a;
Reference 'a' not supported (forward reference in item list)
EXPLAIN SELECT 1 FROM (SELECT 1 as a) HAVING (SELECT a)=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	<derived2>	system	NULL	NULL	NULL	NULL	1	
3	DEPENDENT SUBSELECT								No tables used
2	DERIVED								No tables used
SELECT 1 FROM (SELECT 1 as a) HAVING (SELECT a)=1;
1
1
SELECT (SELECT 1), a;
Unknown column 'a' in 'field list'
SELECT 1 as a FROM (SELECT 1) HAVING (SELECT a)=1;
a
1
SELECT 1 FROM (SELECT (SELECT a));
Unknown column 'a' in 'field list'
drop table if exists t1,t2,t3,t4,t5,t6,t7,t8;
create table t1 (a int);
create table t2 (a int, b int);
create table t3 (a int);
create table t4 (a int, b int);
insert into t1 values (2);
insert into t2 values (1,7),(2,7);
insert into t4 values (4,8),(3,8),(5,9);
select (select a from t1 where t1.a = a1) as a2, (select b from t2 where t2.b=a2) as a1;
Reference 'a1' not supported (forward reference in item list)
select (select a from t1 where t1.a=t2.a), a from t2;
(select a from t1 where t1.a=t2.a)	a
NULL	1
2	2
select (select a from t1 where t1.a=t2.b), a from t2;
(select a from t1 where t1.a=t2.b)	a
NULL	1
NULL	2
select (select a from t1), a from t2;
(select a from t1)	a
2	1
2	2
select (select a from t3), a from t2;
(select a from t3)	a
NULL	1
NULL	2
select * from t2 where t2.a=(select a from t1);
a	b
2	7
insert into t3 values (6),(7),(3);
select * from t2 where t2.b=(select a from t3 order by 1 desc limit 1);
a	b
1	7
2	7
select * from t2 where t2.b=(select a from t3 order by 1 desc limit 1) 
union (select * from t4 order by a limit 2) limit 3;
a	b
1	7
2	7
3	8
select * from t2 where t2.b=(select a from t3 order by 1 desc limit 1)
union (select * from t4 where t4.b=(select max(t2.a)*4 from t2) order by a);
a	b
1	7
2	7
3	8
4	8
explain select * from t2 where t2.b=(select a from t3 order by 1 desc limit 1) 
union (select * from t4 where t4.b=(select max(t2.a)*4 from t2) order by a);
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where
2	SUBSELECT	t3	ALL	NULL	NULL	NULL	NULL	3	Using filesort
3	UNION	t4	ALL	NULL	NULL	NULL	NULL	3	Using where; Using filesort
4	SUBSELECT	t2	ALL	NULL	NULL	NULL	NULL	2	
select (select a from t3 where a<t2.a*4 order by 1 desc limit 1), a from t2;
(select a from t3 where a<t2.a*4 order by 1 desc limit 1)	a
3	1
7	2
select (select t3.a from t3 where a<8 order by 1 desc limit 1), a from 
(select * from t2 where a>1) as tt;
(select t3.a from t3 where a<8 order by 1 desc limit 1)	a
7	2
explain select (select t3.a from t3 where a<8 order by 1 desc limit 1), a from 
(select * from t2 where a>1) as tt;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	<derived3>	system	NULL	NULL	NULL	NULL	1	
3	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	2	Using where
2	SUBSELECT	t3	ALL	NULL	NULL	NULL	NULL	3	Using where; Using filesort
select * from t1 where t1.a=(select t2.a from t2 where t2.b=(select max(a) from t3) order by 1 desc limit 1);
a
2
select * from t1 where t1.a=(select t2.a from t2 where t2.b=(select max(a) from t3 where t3.a > t1.a) order by 1 desc limit 1);
a
2
select * from t1 where t1.a=(select t2.a from t2 where t2.b=(select max(a) from t3 where t3.a < t1.a) order by 1 desc limit 1);
a
select b,(select avg(t2.a+(select min(t3.a) from t3 where t3.a >= t4.a)) from t2) from t4;
b	(select avg(t2.a+(select min(t3.a) from t3 where t3.a >= t4.a)) from t2)
8	7.5000
8	4.5000
9	7.5000
explain select b,(select avg(t2.a+(select min(t3.a) from t3 where t3.a >= t4.a)) from t2) from t4;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t4	ALL	NULL	NULL	NULL	NULL	3	
2	DEPENDENT SUBSELECT	t2	ALL	NULL	NULL	NULL	NULL	2	
3	DEPENDENT SUBSELECT	t3	ALL	NULL	NULL	NULL	NULL	3	Using where
select * from t3 where exists (select * from t2 where t2.b=t3.a);
a
7
select * from t3 where not exists (select * from t2 where t2.b=t3.a);
a
6
3
insert into t4 values (12,7),(1,7),(10,9),(9,6),(7,6),(3,9);
select b,max(a) as ma from t4 group by b having b < (select max(t2.a)
from t2 where t2.b=t4.b);
b	ma
select b,max(a) as ma from t4 group by b having b >= (select max(t2.a)
from t2 where t2.b=t4.b);
b	ma
7	12
create table t5 (a int);
select (select a from t1 where t1.a=t2.a union select a from t5 where t5.a=t2.a), a from t2;
(select a from t1 where t1.a=t2.a union select a from t5 where t5.a=t2.a)	a
NULL	1
2	2
insert into t5 values (5);
select (select a from t1 where t1.a=t2.a union select a from t5 where t5.a=t2.a), a from t2;
(select a from t1 where t1.a=t2.a union select a from t5 where t5.a=t2.a)	a
NULL	1
2	2
insert into t5 values (2);
select (select a from t1 where t1.a=t2.a union select a from t5 where t5.a=t2.a), a from t2;
(select a from t1 where t1.a=t2.a union select a from t5 where t5.a=t2.a)	a
NULL	1
2	2
explain select (select a from t1 where t1.a=t2.a union select a from t5 where t5.a=t2.a), a from t2;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	
2	DEPENDENT SUBSELECT	t1	system	NULL	NULL	NULL	NULL	1	Using where
3	DEPENDENT UNION	t5	ALL	NULL	NULL	NULL	NULL	2	Using where
select (select a from t1 where t1.a=t2.a union all select a from t5 where t5.a=t2.a), a from t2;
Subselect returns more than 1 record
create table t6 (patient_uq int, clinic_uq int, index i1 (clinic_uq));
create table t7( uq int primary key, name char(25));
insert into t7 values(1,"Oblastnaia bolnitsa"),(2,"Bolnitsa Krasnogo Kresta");
insert into t6 values (1,1),(1,2),(2,2),(1,3);
select * from t6 where exists (select * from t7 where uq = clinic_uq);
patient_uq	clinic_uq
1	1
1	2
2	2
select * from t1 where a= (select a from t2,t4 where t2.b=t4.b);
Column: 'a' in field list is ambiguous
drop table if exists t1,t2,t3;
CREATE TABLE t3 (a varchar(20),b char(1) NOT NULL default '0');
INSERT INTO t3 VALUES ('W','a'),('A','c'),('J','b');
CREATE TABLE t2 (a varchar(20),b int NOT NULL default '0');
INSERT INTO t2 VALUES ('W','1'),('A','3'),('J','2');
CREATE TABLE t1 (a varchar(20),b date NOT NULL default '0000-00-00');
INSERT INTO t1 VALUES ('W','1732-02-22'),('A','1735-10-30'),('J','1743-04-13');
SELECT * FROM t1 WHERE b = (SELECT MIN(b) FROM t1);
a	b
W	1732-02-22
SELECT * FROM t2 WHERE b = (SELECT MIN(b) FROM t2);
a	b
W	1
SELECT * FROM t3 WHERE b = (SELECT MIN(b) FROM t3);
a	b
W	a
drop table if exists t8;
CREATE TABLE `t8` (
`pseudo` varchar(35) character set latin1 NOT NULL default '',
`email` varchar(60) character set latin1 NOT NULL default '',
PRIMARY KEY  (`pseudo`),
UNIQUE KEY `email` (`email`)
) TYPE=MyISAM CHARSET=latin1 ROW_FORMAT=DYNAMIC;
INSERT INTO t8 (pseudo,email) VALUES ('joce','test');
INSERT INTO t8 (pseudo,email) VALUES ('joce1','test1');
INSERT INTO t8 (pseudo,email) VALUES ('2joce1','2test1');
EXPLAIN SELECT pseudo,(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce')) FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce');
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t8	const	PRIMARY	PRIMARY	35	const	1	
4	SUBSELECT	t8	const	PRIMARY	PRIMARY	35	const	1	
2	SUBSELECT	t8	const	PRIMARY	PRIMARY	35	const	1	
3	SUBSELECT	t8	const	PRIMARY	PRIMARY	35	const	1	
SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo,email FROM
t8 WHERE pseudo='joce');
Subselect returns more than 1 field
SELECT pseudo FROM t8 WHERE pseudo=(SELECT * FROM t8 WHERE
pseudo='joce');
Subselect returns more than 1 field
SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce');
pseudo
joce
SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo LIKE '%joce%');
Subselect returns more than 1 record
drop table if exists t1,t2,t3,t4,t5,t6,t7,t8;
CREATE TABLE `t1` (
`topic` mediumint(8) unsigned NOT NULL default '0',
`date` date NOT NULL default '0000-00-00',
`pseudo` varchar(35) character set latin1 NOT NULL default '',
PRIMARY KEY  (`pseudo`,`date`,`topic`),
KEY `topic` (`topic`)
) TYPE=MyISAM ROW_FORMAT=DYNAMIC;
INSERT INTO t1 (topic,date,pseudo) VALUES
('43506','2002-10-02','joce'),('40143','2002-08-03','joce');
EXPLAIN SELECT DISTINCT date FROM t1 WHERE date='2002-08-03';
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index	NULL	PRIMARY	41	NULL	2	Using where; Using index
EXPLAIN SELECT (SELECT DISTINCT date FROM t1 WHERE date='2002-08-03');
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY								No tables used
2	SUBSELECT	t1	index	NULL	PRIMARY	41	NULL	2	Using where; Using index
SELECT DISTINCT date FROM t1 WHERE date='2002-08-03';
date
2002-08-03
SELECT (SELECT DISTINCT date FROM t1 WHERE date='2002-08-03');
(SELECT DISTINCT date FROM t1 WHERE date='2002-08-03')
2002-08-03
SELECT 1 FROM t1 WHERE 1=(SELECT 1 UNION SELECT 1) UNION ALL SELECT 1;
1
1
1
1
SELECT 1 FROM t1 WHERE 1=(SELECT 1 UNION ALL SELECT 1) UNION SELECT 1;
Subselect returns more than 1 record
EXPLAIN SELECT 1 FROM t1 WHERE 1=(SELECT 1 UNION SELECT 1);
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t1	index	NULL	topic	3	NULL	2	Using index
2	SUBSELECT								No tables used
3	UNION								No tables used
drop table t1;
CREATE TABLE `t1` (
`numeropost` mediumint(8) unsigned NOT NULL auto_increment,
`maxnumrep` int(10) unsigned NOT NULL default '0',
PRIMARY KEY  (`numeropost`),
UNIQUE KEY `maxnumrep` (`maxnumrep`)
) TYPE=MyISAM ROW_FORMAT=FIXED;
INSERT INTO t1 (numeropost,maxnumrep) VALUES (40143,1),(43506,2);
CREATE TABLE `t2` (
`mot` varchar(30) NOT NULL default '',
`topic` mediumint(8) unsigned NOT NULL default '0',
`date` date NOT NULL default '0000-00-00',
`pseudo` varchar(35) NOT NULL default '',
PRIMARY KEY  (`mot`,`pseudo`,`date`,`topic`)
) TYPE=MyISAM ROW_FORMAT=DYNAMIC;
INSERT INTO t2 (mot,topic,date,pseudo) VALUES ('joce','40143','2002-10-22','joce'), ('joce','43506','2002-10-22','joce');
select numeropost as a FROM t1 GROUP BY (SELECT 1 FROM t1 HAVING a=1);
a
40143
SELECT numeropost,maxnumrep FROM t1 WHERE exists (SELECT 1 FROM t2 WHERE (mot='joce') AND date >= '2002-10-21' AND t1.numeropost = t2.topic) ORDER BY maxnumrep DESC LIMIT 0, 20;
numeropost	maxnumrep
43506	2
40143	1
SELECT (SELECT 1) as a FROM (SELECT 1 FROM t1 HAVING a=1);
Unknown column 'a' in 'having clause'
drop table t1, t2;
drop table if exists t1;
CREATE TABLE `t1` (
`numeropost` mediumint(8) unsigned NOT NULL auto_increment,
`maxnumrep` int(10) unsigned NOT NULL default '0',
PRIMARY KEY  (`numeropost`),
UNIQUE KEY `maxnumrep` (`maxnumrep`)
) TYPE=MyISAM ROW_FORMAT=FIXED;
INSERT INTO t1 (numeropost,maxnumrep) VALUES (1,0),(2,1);
select numeropost as a FROM t1 GROUP BY (SELECT 1 FROM t1 HAVING a=1);
Subselect returns more than 1 record
select numeropost as a FROM t1 ORDER BY (SELECT 1 FROM t1 HAVING a=1);
Subselect returns more than 1 record
drop table t1;
CREATE TABLE t1 (field char(1) NOT NULL DEFAULT 'b');
INSERT INTO t1 VALUES ();
SELECT field FROM t1 WHERE 1=(SELECT 1 UNION ALL SELECT 1 FROM (SELECT 1) HAVING field='b');
Subselect returns more than 1 record
drop table t1;
CREATE TABLE `t1` (
`numeropost` mediumint(8) unsigned NOT NULL default '0',
`numreponse` int(10) unsigned NOT NULL auto_increment,
`pseudo` varchar(35) NOT NULL default '',
PRIMARY KEY  (`numeropost`,`numreponse`),
UNIQUE KEY `numreponse` (`numreponse`),
KEY `pseudo` (`pseudo`,`numeropost`)
) TYPE=MyISAM;
SELECT (SELECT numeropost FROM t1 HAVING numreponse=a),numreponse FROM (SELECT * FROM t1) as a;
Reference 'numreponse' not supported (forward reference in item list)
SELECT numreponse, (SELECT numeropost FROM t1 HAVING numreponse=a) FROM (SELECT * FROM t1) as a;
Unknown column 'a' in 'having clause'
SELECT numreponse, (SELECT numeropost FROM t1 HAVING numreponse=1) FROM (SELECT * FROM t1) as a;
numreponse	(SELECT numeropost FROM t1 HAVING numreponse=1)
INSERT INTO t1 (numeropost,numreponse,pseudo) VALUES (1,1,'joce'),(1,2,'joce'),(1,3,'test');
EXPLAIN SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
Subselect returns more than 1 record
EXPLAIN SELECT MAX(numreponse) FROM t1 WHERE numeropost='1';
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE								Select tables optimized away
EXPLAIN SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT MAX(numreponse) FROM t1 WHERE numeropost='1');
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	
2	SUBSELECT								Select tables optimized away
drop table t1;
CREATE TABLE t1 (a int(1));
INSERT INTO t1 VALUES (1);
SELECT 1 FROM (SELECT a FROM t1) HAVING (SELECT a)=1;
1
1
drop table t1;
create table t1 (a int NOT NULL, b int, primary key (a));
create table t2 (a int NOT NULL, b int, primary key (a));
insert into t1 values (0, 10),(1, 11),(2, 12);
insert into t2 values (1, 21),(2, 22),(3, 23);
select * from t1;
a	b
0	10
1	11
2	12
update t1 set b= (select b from t2 where t1.a = t2.a);
select * from t1;
a	b
0	NULL
1	21
2	22
drop table t1, t2;
create table t1 (a int NOT NULL, b int, primary key (a));
create table t2 (a int NOT NULL, b int, primary key (a));
insert into t1 values (0, 10),(1, 11),(2, 12);
insert into t2 values (1, 21),(2, 12),(3, 23);
select * from t1;
a	b
0	10
1	11
2	12
select * from t1 where b = (select b from t2 where t1.a = t2.a);
a	b
2	12
delete from t1 where b = (select b from t2 where t1.a = t2.a);
select * from t1;
a	b
0	10
1	11
drop table t1, t2;
drop table if exists t11, t12, t2;
create table t11 (a int NOT NULL, b int, primary key (a));
create table t12 (a int NOT NULL, b int, primary key (a));
create table t2 (a int NOT NULL, b int, primary key (a));
insert into t11 values (0, 10),(1, 11),(2, 12);
insert into t12 values (33, 10),(22, 11),(2, 12);
insert into t2 values (1, 21),(2, 12),(3, 23);
select * from t11;
a	b
0	10
1	11
2	12
select * from t12;
a	b
33	10
22	11
2	12
delete t11.*, t12.* from t11,t12 where t11.a = t12.a and t11.b = (select b from t2 where t11.a = t2.a);
select * from t11;
a	b
0	10
1	11
select * from t12;
a	b
33	10
22	11
drop table t11, t12, t2;
CREATE TABLE t1 (x int);
create table t2 (a int);
insert into t2 values (1);
INSERT INTO t1 (x) VALUES ((SELECT a FROM t2));
select * from t1;
x
1
insert into t2 values (1);
INSERT DELAYED INTO t1 (x) VALUES ((SELECT SUM(a) FROM t2));
select * from t1;
x
1
2
INSERT INTO t1 (x) select (SELECT SUM(a)+1 FROM t2) FROM t2;
select * from t1;
x
1
2
3
3
INSERT INTO t1 (x) select (SELECT SUM(x)+2 FROM t1) FROM t2;
INSERT TABLE 't1' isn't allowed in FROM table list
INSERT DELAYED INTO t1 (x) VALUES ((SELECT SUM(x) FROM t1));
select * from t1;
x
1
2
3
3
9
drop table t1, t2;
CREATE TABLE t1 (x int not null, y int, primary key (x));
create table t2 (a int);
insert into t2 values (1);
select * from t1;
x	y
replace into t1 (x, y) VALUES ((SELECT a FROM t2), (SELECT a+1 FROM t2));
select * from t1;
x	y
1	2
replace into t1 (x, y) VALUES ((SELECT a FROM t2), (SELECT a+2 FROM t2));
select * from t1;
x	y
1	3
replace DELAYED into t1 (x, y) VALUES ((SELECT a+3 FROM t2), (SELECT a FROM t2));
select * from t1;
x	y
1	3
4	1
replace DELAYED into t1 (x, y) VALUES ((SELECT a+3 FROM t2), (SELECT a+1 FROM t2));
select * from t1;
x	y
1	3
4	2
replace LOW_PRIORITY into t1 (x, y) VALUES ((SELECT a+1 FROM t2), (SELECT a FROM t2));
select * from t1;
x	y
1	3
4	2
2	1
drop table t1, t2;