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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
drop table if exists t1,t2,t3,t4,t5,attend,clinic,inscrit;
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=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 where used
2 SUBSELECT t3 ALL NULL NULL NULL NULL 3 Using filesort
3 UNION t4 ALL NULL NULL NULL NULL 3 where used; 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
3 DERIVED t2 ALL NULL NULL NULL NULL 2 where used
1 PRIMARY <derived3> system NULL NULL NULL NULL 1
2 SUBSELECT t3 ALL NULL NULL NULL NULL 3 where used; 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 where used
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 where used
3 DEPENDENT UNION t5 ALL NULL NULL NULL NULL 2 where used
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 attend (patient_uq int, clinic_uq int, index i1 (clinic_uq));
create table clinic( uq int primary key, name char(25));
insert into clinic values(1,"Oblastnaia bolnitsa"),(2,"Bolnitsa Krasnogo Kresta");
insert into attend values (1,1),(1,2),(2,2),(1,3);
select * from attend where exists (select * from clinic 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 inscrit;
CREATE TABLE `inscrit` (
`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 inscrit (pseudo,email) VALUES ('joce','test');
INSERT INTO inscrit (pseudo,email) VALUES ('joce1','test1');
INSERT INTO inscrit (pseudo,email) VALUES ('2joce1','2test1');
EXPLAIN SELECT pseudo,(SELECT email FROM inscrit WHERE pseudo=(SELECT pseudo FROM inscrit WHERE pseudo='joce')) FROM inscrit WHERE pseudo=(SELECT pseudo FROM inscrit WHERE pseudo='joce');
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY inscrit const PRIMARY PRIMARY 35 const 1
4 SUBSELECT inscrit const PRIMARY PRIMARY 35 const 1
2 SUBSELECT inscrit const PRIMARY PRIMARY 35 const 1
3 SUBSELECT inscrit const PRIMARY PRIMARY 35 const 1
SELECT pseudo FROM inscrit WHERE pseudo=(SELECT pseudo,email FROM
inscrit WHERE pseudo='joce');
Subselect returns more than 1 field
SELECT pseudo FROM inscrit WHERE pseudo=(SELECT * FROM inscrit WHERE
pseudo='joce');
Subselect returns more than 1 field
SELECT pseudo FROM inscrit WHERE pseudo=(SELECT pseudo FROM inscrit WHERE pseudo='joce');
pseudo
joce
SELECT pseudo FROM inscrit WHERE pseudo=(SELECT pseudo FROM inscrit WHERE pseudo LIKE '%joce%');
Subselect returns more than 1 record
drop table if exists t1,t2,t3,t4,t5,attend,clinic,inscrit;
drop table if exists searchconthardwarefr3;
CREATE TABLE `searchconthardwarefr3` (
`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 searchconthardwarefr3 (topic,date,pseudo) VALUES
('43506','2002-10-02','joce'),('40143','2002-08-03','joce');
EXPLAIN SELECT DISTINCT date FROM searchconthardwarefr3 WHERE date='2002-08-03';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE searchconthardwarefr3 index NULL PRIMARY 41 NULL 2 where used; Using index
EXPLAIN SELECT (SELECT DISTINCT date FROM searchconthardwarefr3 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 searchconthardwarefr3 index NULL PRIMARY 41 NULL 2 where used; Using index
SELECT DISTINCT date FROM searchconthardwarefr3 WHERE date='2002-08-03';
date
2002-08-03
SELECT (SELECT DISTINCT date FROM searchconthardwarefr3 WHERE date='2002-08-03');
(SELECT DISTINCT date FROM searchconthardwarefr3 WHERE date='2002-08-03')
2002-08-03
SELECT 1 FROM searchconthardwarefr3 WHERE 1=(SELECT 1 UNION SELECT 1) UNION ALL SELECT 1;
1
1
1
1
SELECT 1 FROM searchconthardwarefr3 WHERE 1=(SELECT 1 UNION ALL SELECT 1) UNION SELECT 1;
Subselect returns more than 1 record
EXPLAIN SELECT 1 FROM searchconthardwarefr3 WHERE 1=(SELECT 1 UNION SELECT 1);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY searchconthardwarefr3 index NULL topic 3 NULL 2 Using index
2 SUBSELECT No tables used
3 UNION No tables used
drop table searchconthardwarefr3;
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