drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t11,t12; select (select 2); (select 2) 2 explain select (select 2); id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY NULL NULL NULL NULL NULL NULL NULL No tables used Warnings: Note 1247 Select 2 was reduced during optimisation SELECT (SELECT 1) UNION SELECT (SELECT 2); (SELECT 1) 1 2 explain SELECT (SELECT 1) UNION SELECT (SELECT 2); id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY NULL NULL NULL NULL NULL NULL NULL No tables used 3 UNION NULL NULL NULL NULL NULL NULL NULL No tables used Warnings: Note 1247 Select 2 was reduced during optimisation Note 1247 Select 4 was reduced during optimisation SELECT (SELECT (SELECT 0 UNION SELECT 0)); (SELECT (SELECT 0 UNION SELECT 0)) 0 explain SELECT (SELECT (SELECT 0 UNION SELECT 0)); id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY NULL NULL NULL NULL NULL NULL NULL No tables used 3 SUBQUERY NULL NULL NULL NULL NULL NULL NULL No tables used 4 UNION NULL NULL NULL NULL NULL NULL NULL No tables used Warnings: Note 1247 Select 2 was reduced during optimisation SELECT (SELECT 1 FROM (SELECT 1) as b HAVING a=1) as a; ERROR 42S22: Reference 'a' not supported (forward reference in item list) SELECT (SELECT 1 FROM (SELECT 1) as b HAVING b=1) as a,(SELECT 1 FROM (SELECT 1) as c HAVING a=1) as b; ERROR 42S22: Reference 'b' not supported (forward reference in item list) SELECT (SELECT 1),MAX(1) FROM (SELECT 1) as a; (SELECT 1) MAX(1) 1 1 SELECT (SELECT a) as a; ERROR 42S22: Reference 'a' not supported (forward reference in item list) EXPLAIN SELECT 1 FROM (SELECT 1 as a) as b 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 SUBQUERY NULL NULL NULL NULL NULL NULL NULL No tables used 2 DERIVED NULL NULL NULL NULL NULL NULL NULL No tables used SELECT 1 FROM (SELECT 1 as a) as b HAVING (SELECT a)=1; 1 1 SELECT (SELECT 1), a; ERROR 42S22: Unknown column 'a' in 'field list' SELECT 1 as a FROM (SELECT 1) as b HAVING (SELECT a)=1; a 1 SELECT 1 FROM (SELECT (SELECT a) b) c; ERROR 42S22: Unknown column 'a' in 'field list' SELECT * FROM (SELECT 1 as id) b WHERE id IN (SELECT * FROM (SELECT 1 as id) c ORDER BY id); id 1 SELECT * FROM (SELECT 1) a WHERE 1 IN (SELECT 1,1); ERROR 21000: Cardinality error (more/less than 1 columns) SELECT 1 IN (SELECT 1); 1 IN (SELECT 1) 1 SELECT 1 FROM (SELECT 1 as a) b WHERE 1 IN (SELECT (SELECT a)); 1 1 select (SELECT 1 FROM (SELECT 1) a PROCEDURE ANALYSE(1)); ERROR HY000: Wrong usage of PROCEDURE and subquery SELECT 1 FROM (SELECT 1) a PROCEDURE ANALYSE((SELECT 1)); ERROR HY000: Incorrect parameters to procedure 'ANALYSE' SELECT (SELECT 1) as a FROM (SELECT 1) b WHERE (SELECT a) IS NULL; a SELECT (SELECT 1) as a FROM (SELECT 1) b WHERE (SELECT a) IS NOT NULL; a 1 SELECT (SELECT 1,2,3) = ROW(1,2,3); (SELECT 1,2,3) = ROW(1,2,3) 1 SELECT (SELECT 1,2,3) = ROW(1,2,1); (SELECT 1,2,3) = ROW(1,2,1) 0 SELECT (SELECT 1,2,3) < ROW(1,2,1); (SELECT 1,2,3) < ROW(1,2,1) 0 SELECT (SELECT 1,2,3) > ROW(1,2,1); (SELECT 1,2,3) > ROW(1,2,1) 1 SELECT (SELECT 1,2,3) = ROW(1,2,NULL); (SELECT 1,2,3) = ROW(1,2,NULL) NULL SELECT ROW(1,2,3) = (SELECT 1,2,3); ROW(1,2,3) = (SELECT 1,2,3) 1 SELECT ROW(1,2,3) = (SELECT 1,2,1); ROW(1,2,3) = (SELECT 1,2,1) 0 SELECT ROW(1,2,3) < (SELECT 1,2,1); ROW(1,2,3) < (SELECT 1,2,1) 0 SELECT ROW(1,2,3) > (SELECT 1,2,1); ROW(1,2,3) > (SELECT 1,2,1) 1 SELECT ROW(1,2,3) = (SELECT 1,2,NULL); ROW(1,2,3) = (SELECT 1,2,NULL) NULL SELECT (SELECT 1.5,2,'a') = ROW(1.5,2,'a'); (SELECT 1.5,2,'a') = ROW(1.5,2,'a') 1 SELECT (SELECT 1.5,2,'a') = ROW(1.5,2,'b'); (SELECT 1.5,2,'a') = ROW(1.5,2,'b') 0 SELECT (SELECT 1.5,2,'a') = ROW('b',2,'b'); (SELECT 1.5,2,'a') = ROW('b',2,'b') 0 SELECT (SELECT 'b',2,'a') = ROW(1.5,2,'a'); (SELECT 'b',2,'a') = ROW(1.5,2,'a') 0 SELECT (SELECT 1.5,2,'a') = ROW(1.5,'c','a'); (SELECT 1.5,2,'a') = ROW(1.5,'c','a') 0 SELECT (SELECT 1.5,'c','a') = ROW(1.5,2,'a'); (SELECT 1.5,'c','a') = ROW(1.5,2,'a') 0 SELECT (SELECT * FROM (SELECT 'test' a,'test' b) a); ERROR 21000: Cardinality error (more/less than 1 columns) SELECT 1 as a,(SELECT a+a) b,(SELECT b); a b (SELECT b) 1 2 2 create table t1 (a int); create table t2 (a int, b int); create table t3 (a int); create table t4 (a int not null, b int not null); 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; ERROR 42S22: 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 SUBQUERY t3 ALL NULL NULL NULL NULL 3 Using filesort 3 UNION t4 ALL NULL NULL NULL NULL 3 Using where; Using filesort 4 SUBQUERY 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 SUBQUERY 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 SUBQUERY t2 ALL NULL NULL NULL NULL 2 3 DEPENDENT SUBQUERY 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 select * from t3 where a in (select b from t2); a 7 select * from t3 where a not in (select b from t2); a 6 3 select * from t3 where a = some (select b from t2); a 7 select * from t3 where a <> any (select b from t2); a 6 3 select * from t3 where a = all (select b from t2); a 7 select * from t3 where a <> all (select b from t2); a 6 3 insert into t2 values (100, 5); select * from t3 where a < any (select b from t2); a 6 3 select * from t3 where a < all (select b from t2); a 3 select * from t3 where a >= any (select b from t2); a 6 7 select * from t3 where a >= all (select b from t2); a 7 delete from t2 where a=100; select * from t3 where a in (select a,b from t2); ERROR 21000: Cardinality error (more/less than 1 columns) select * from t3 where a in (select * from t2); ERROR 21000: Cardinality error (more/less than 1 columns) insert into t4 values (12,7),(1,7),(10,9),(9,6),(7,6),(3,9),(1,10); 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 insert into t2 values (2,10); select b,max(a) as ma from t4 group by b having ma < (select max(t2.a) from t2 where t2.b=t4.b); b ma 10 1 delete from t2 where a=2 and b=10; 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 SUBQUERY t1 system NULL NULL NULL NULL 1 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; ERROR 21000: 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 explain select * from t6 where exists (select * from t7 where uq = clinic_uq); id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t6 ALL NULL NULL NULL NULL 4 Using where 2 DEPENDENT SUBQUERY t7 eq_ref PRIMARY PRIMARY 4 test.t6.clinic_uq 1 select * from t1 where a= (select a from t2,t4 where t2.b=t4.b); ERROR 23000: 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 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 SUBQUERY t8 const PRIMARY PRIMARY 35 1 2 SUBQUERY t8 const PRIMARY PRIMARY 35 const 1 3 SUBQUERY t8 const PRIMARY PRIMARY 35 1 SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo,email FROM t8 WHERE pseudo='joce'); ERROR 21000: Cardinality error (more/less than 1 columns) SELECT pseudo FROM t8 WHERE pseudo=(SELECT * FROM t8 WHERE pseudo='joce'); ERROR 21000: Cardinality error (more/less than 1 columns) 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%'); ERROR 21000: 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 NULL NULL NULL NULL NULL NULL NULL No tables used 2 SUBQUERY 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; ERROR 21000: 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 SUBQUERY NULL NULL NULL NULL NULL NULL NULL No tables used 3 UNION NULL NULL NULL NULL NULL NULL NULL 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) b; ERROR 42S22: Unknown column 'a' in 'having clause' SELECT 1 IN (SELECT 1 FROM t2 HAVING a); ERROR 42S22: Unknown column 'a' in 'having clause' SELECT * from t2 where topic IN (SELECT topic FROM t2 GROUP BY topic); mot topic date pseudo joce 40143 2002-10-22 joce joce 43506 2002-10-22 joce SELECT * from t2 where topic IN (SELECT topic FROM t2 GROUP BY topic HAVING topic < 4100); mot topic date pseudo SELECT * from t2 where topic IN (SELECT SUM(topic) FROM t1); mot topic date pseudo SELECT * from t2 where topic = any (SELECT topic FROM t2 GROUP BY topic); mot topic date pseudo joce 40143 2002-10-22 joce joce 43506 2002-10-22 joce SELECT * from t2 where topic = any (SELECT topic FROM t2 GROUP BY topic HAVING topic < 4100); mot topic date pseudo SELECT * from t2 where topic = any (SELECT SUM(topic) FROM t1); mot topic date pseudo SELECT * from t2 where topic = all (SELECT topic FROM t2 GROUP BY topic); mot topic date pseudo SELECT * from t2 where topic = all (SELECT topic FROM t2 GROUP BY topic HAVING topic < 4100); mot topic date pseudo joce 40143 2002-10-22 joce joce 43506 2002-10-22 joce SELECT *, topic = all (SELECT topic FROM t2 GROUP BY topic HAVING topic < 4100) from t2; mot topic date pseudo topic = all (SELECT topic FROM t2 GROUP BY topic HAVING topic < 4100) joce 40143 2002-10-22 joce 1 joce 43506 2002-10-22 joce 1 SELECT * from t2 where topic = all (SELECT SUM(topic) FROM t2); mot topic date pseudo SELECT * from t2 where topic <> any (SELECT SUM(topic) FROM t2); mot topic date pseudo joce 40143 2002-10-22 joce joce 43506 2002-10-22 joce SELECT * from t2 where topic IN (SELECT topic FROM t2 GROUP BY topic HAVING topic < 41000); mot topic date pseudo joce 40143 2002-10-22 joce SELECT * from t2 where topic = any (SELECT topic FROM t2 GROUP BY topic HAVING topic < 41000); mot topic date pseudo joce 40143 2002-10-22 joce SELECT * from t2 where topic = all (SELECT topic FROM t2 GROUP BY topic HAVING topic < 41000); mot topic date pseudo joce 40143 2002-10-22 joce SELECT *, topic = all (SELECT topic FROM t2 GROUP BY topic HAVING topic < 41000) from t2; mot topic date pseudo topic = all (SELECT topic FROM t2 GROUP BY topic HAVING topic < 41000) joce 40143 2002-10-22 joce 1 joce 43506 2002-10-22 joce 0 drop table t1,t2; 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); ERROR 21000: Subselect returns more than 1 record select numeropost as a FROM t1 ORDER BY (SELECT 1 FROM t1 HAVING a=1); ERROR 21000: Subselect returns more than 1 record drop table t1; create table t1 (a int); insert into t1 values (1),(2),(3); (select * from t1) union (select * from t1) order by (select a from t1 limit 1); a 1 2 3 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) a HAVING field='b'); ERROR 21000: 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; ERROR 42S22: Reference 'numreponse' not supported (forward reference in item list) SELECT numreponse, (SELECT numeropost FROM t1 HAVING numreponse=a) FROM (SELECT * FROM t1) as a; ERROR 42S22: 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'); ERROR 21000: 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 NULL NULL NULL NULL NULL NULL NULL 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 SUBQUERY NULL NULL NULL NULL NULL NULL NULL 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) b HAVING (SELECT b.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 t1); ERROR HY000: You can't specify target table 't1' for update in FROM clause update t1 set b= (select b from t2); ERROR 21000: Subselect returns more than 1 record 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 t1); ERROR HY000: You can't specify target table 't1' for update in FROM clause delete from t1 where b = (select b from t2); ERROR 21000: Subselect returns more than 1 record 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; 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 t12 where t11.a = t12.a); ERROR HY000: You can't specify target table 't12' for update in FROM clause delete t11.*, t12.* from t11,t12 where t11.a = t12.a and t11.b = (select b from t2); ERROR 21000: Subselect returns more than 1 record 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); create table t3 (b int); insert into t2 values (1); insert into t3 values (1),(2); INSERT INTO t1 (x) VALUES ((SELECT x FROM t1)); ERROR HY000: You can't specify target table 't1' for update in FROM clause INSERT INTO t1 (x) VALUES ((SELECT b FROM t3)); ERROR 21000: Subselect returns more than 1 record 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; ERROR HY000: You can't specify target table 't1' for update in FROM clause INSERT DELAYED INTO t1 (x) VALUES ((SELECT SUM(x) FROM t2)); ERROR 42S22: Unknown column 'x' in 'field list' INSERT DELAYED INTO t1 (x) VALUES ((SELECT SUM(a) FROM t2)); select * from t1; x 1 2 3 3 2 drop table t1, t2, t3; CREATE TABLE t1 (x int not null, y int, primary key (x)); create table t2 (a int); create table t3 (a int); insert into t2 values (1); insert into t3 values (1),(2); select * from t1; x y replace into t1 (x, y) VALUES ((SELECT x FROM t1), (SELECT a+1 FROM t2)); ERROR HY000: You can't specify target table 't1' for update in FROM clause replace into t1 (x, y) VALUES ((SELECT a FROM t3), (SELECT a+1 FROM t2)); ERROR 21000: Subselect returns more than 1 record 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, t3; SELECT * FROM (SELECT 1) b WHERE 1 IN (SELECT *); ERROR HY000: No tables used CREATE TABLE t2 (id int(11) default NULL, KEY id (id)) TYPE=MyISAM CHARSET=latin1; INSERT INTO t2 VALUES (1),(2); SELECT * FROM t2 WHERE id IN (SELECT 1); id 1 EXPLAIN SELECT * FROM t2 WHERE id IN (SELECT 1); id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t2 ref id id 5 const 1 Using where; Using index Warnings: Note 1247 Select 2 was reduced during optimisation SELECT * FROM t2 WHERE id IN (SELECT 1 UNION SELECT 3); id 1 SELECT * FROM t2 WHERE id IN (SELECT 1+(select 1)); id 2 EXPLAIN SELECT * FROM t2 WHERE id IN (SELECT 1+(select 1)); id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t2 ref id id 5 const 1 Using where; Using index 3 SUBQUERY NULL NULL NULL NULL NULL NULL NULL No tables used Warnings: Note 1247 Select 3 was reduced during optimisation Note 1247 Select 2 was reduced during optimisation EXPLAIN SELECT * FROM t2 WHERE id IN (SELECT 1 UNION SELECT 3); id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t2 index NULL id 5 NULL 2 Using where; Using index 2 DEPENDENT SUBQUERY NULL NULL NULL NULL NULL NULL NULL No tables used 3 DEPENDENT UNION NULL NULL NULL NULL NULL NULL NULL No tables used SELECT * FROM t2 WHERE id IN (SELECT 5 UNION SELECT 3); id SELECT * FROM t2 WHERE id IN (SELECT 5 UNION SELECT 2); id 2 INSERT INTO t2 VALUES ((SELECT * FROM t2)); ERROR HY000: You can't specify target table 't2' for update in FROM clause INSERT INTO t2 VALUES ((SELECT id FROM t2)); ERROR HY000: You can't specify target table 't2' for update in FROM clause SELECT * FROM t2; id 1 2 CREATE TABLE t1 (id int(11) default NULL, KEY id (id)) TYPE=MyISAM CHARSET=latin1; INSERT INTO t1 values (1),(1); UPDATE t2 SET id=(SELECT * FROM t1); ERROR 21000: Subselect returns more than 1 record drop table t2, t1; create table t1 (a int); insert into t1 values (1),(2),(3); select 1 IN (SELECT * from t1); 1 IN (SELECT * from t1) 1 select 10 IN (SELECT * from t1); 10 IN (SELECT * from t1) 0 select NULL IN (SELECT * from t1); NULL IN (SELECT * from t1) NULL update t1 set a=NULL where a=2; select 1 IN (SELECT * from t1); 1 IN (SELECT * from t1) 1 select 3 IN (SELECT * from t1); 3 IN (SELECT * from t1) 1 select 10 IN (SELECT * from t1); 10 IN (SELECT * from t1) NULL select 1 > ALL (SELECT * from t1); 1 > ALL (SELECT * from t1) 0 select 10 > ALL (SELECT * from t1); 10 > ALL (SELECT * from t1) NULL select 1 > ANY (SELECT * from t1); 1 > ANY (SELECT * from t1) NULL select 10 > ANY (SELECT * from t1); 10 > ANY (SELECT * from t1) 1 drop table t1; create table t1 (a varchar(20)); insert into t1 values ('A'),('BC'),('DEF'); select 'A' IN (SELECT * from t1); 'A' IN (SELECT * from t1) 1 select 'XYZS' IN (SELECT * from t1); 'XYZS' IN (SELECT * from t1) 0 select NULL IN (SELECT * from t1); NULL IN (SELECT * from t1) NULL update t1 set a=NULL where a='BC'; select 'A' IN (SELECT * from t1); 'A' IN (SELECT * from t1) 1 select 'DEF' IN (SELECT * from t1); 'DEF' IN (SELECT * from t1) 1 select 'XYZS' IN (SELECT * from t1); 'XYZS' IN (SELECT * from t1) NULL select 'A' > ALL (SELECT * from t1); 'A' > ALL (SELECT * from t1) 0 select 'XYZS' > ALL (SELECT * from t1); 'XYZS' > ALL (SELECT * from t1) NULL select 'A' > ANY (SELECT * from t1); 'A' > ANY (SELECT * from t1) NULL select 'XYZS' > ANY (SELECT * from t1); 'XYZS' > ANY (SELECT * from t1) 1 drop table t1; create table t1 (a float); insert into t1 values (1.5),(2.5),(3.5); select 1.5 IN (SELECT * from t1); 1.5 IN (SELECT * from t1) 1 select 10.5 IN (SELECT * from t1); 10.5 IN (SELECT * from t1) 0 select NULL IN (SELECT * from t1); NULL IN (SELECT * from t1) NULL update t1 set a=NULL where a=2.5; select 1.5 IN (SELECT * from t1); 1.5 IN (SELECT * from t1) 1 select 3.5 IN (SELECT * from t1); 3.5 IN (SELECT * from t1) 1 select 10.5 IN (SELECT * from t1); 10.5 IN (SELECT * from t1) NULL select 1.5 > ALL (SELECT * from t1); 1.5 > ALL (SELECT * from t1) 0 select 10.5 > ALL (SELECT * from t1); 10.5 > ALL (SELECT * from t1) NULL select 1.5 > ANY (SELECT * from t1); 1.5 > ANY (SELECT * from t1) NULL select 10.5 > ANY (SELECT * from t1); 10.5 > ANY (SELECT * from t1) 1 explain select (select a+1) from t1; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t1 ALL NULL NULL NULL NULL 3 Warnings: Note 1247 Select 2 was reduced during optimisation select (select a+1) from t1; (select a+1) 2.5 NULL 4.5 drop table t1; CREATE TABLE t1 (a int(11) NOT NULL default '0', PRIMARY KEY (a)); CREATE TABLE t2 (a int(11) default '0', INDEX (a)); INSERT INTO t1 VALUES (1),(2),(3),(4); INSERT INTO t2 VALUES (1),(2),(3); SELECT t1.a, t1.a in (select t2.a from t2) FROM t1; a t1.a in (select t2.a from t2) 1 1 2 1 3 1 4 0 explain SELECT t1.a, t1.a in (select t2.a from t2) FROM t1; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t1 index NULL PRIMARY 4 NULL 4 Using index 2 DEPENDENT SUBQUERY t2 ref_or_null a a 5 const 2 Using where; Using index drop table t1,t2; create table t1 (a float); select 10.5 IN (SELECT * from t1 LIMIT 1); ERROR 42000: This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery' select 10.5 IN (SELECT * from t1 LIMIT 1 UNION SELECT 1.5); ERROR 42000: This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery' drop table t1; create table t1 (a int, b int, c varchar(10)); create table t2 (a int); insert into t1 values (1,2,'a'),(2,3,'b'),(3,4,'c'); insert into t2 values (1),(2),(NULL); select a, (select a,b,c from t1 where t1.a=t2.a) = ROW(a,2,'a'),(select c from t1 where a=t2.a) from t2; a (select a,b,c from t1 where t1.a=t2.a) = ROW(a,2,'a') (select c from t1 where a=t2.a) 1 1 a 2 0 b NULL NULL NULL select a, (select a,b,c from t1 where t1.a=t2.a) = ROW(a,3,'b'),(select c from t1 where a=t2.a) from t2; a (select a,b,c from t1 where t1.a=t2.a) = ROW(a,3,'b') (select c from t1 where a=t2.a) 1 0 a 2 1 b NULL NULL NULL select a, (select a,b,c from t1 where t1.a=t2.a) = ROW(a,4,'c'),(select c from t1 where a=t2.a) from t2; a (select a,b,c from t1 where t1.a=t2.a) = ROW(a,4,'c') (select c from t1 where a=t2.a) 1 0 a 2 0 b NULL NULL NULL drop table t1,t2; create table t1 (a int, b real, c varchar(10)); insert into t1 values (1, 1, 'a'), (2,2,'b'), (NULL, 2, 'b'); select ROW(1, 1, 'a') IN (select a,b,c from t1); ROW(1, 1, 'a') IN (select a,b,c from t1) 1 select ROW(1, 2, 'a') IN (select a,b,c from t1); ROW(1, 2, 'a') IN (select a,b,c from t1) NULL select ROW(1, 1, 'a') IN (select b,a,c from t1); ROW(1, 1, 'a') IN (select b,a,c from t1) 1 select ROW(1, 1, 'a') IN (select a,b,c from t1 where a is not null); ROW(1, 1, 'a') IN (select a,b,c from t1 where a is not null) 1 select ROW(1, 2, 'a') IN (select a,b,c from t1 where a is not null); ROW(1, 2, 'a') IN (select a,b,c from t1 where a is not null) 0 select ROW(1, 1, 'a') IN (select b,a,c from t1 where a is not null); ROW(1, 1, 'a') IN (select b,a,c from t1 where a is not null) 1 select ROW(1, 1, 'a') IN (select a,b,c from t1 where c='b' or c='a'); ROW(1, 1, 'a') IN (select a,b,c from t1 where c='b' or c='a') 1 select ROW(1, 2, 'a') IN (select a,b,c from t1 where c='b' or c='a'); ROW(1, 2, 'a') IN (select a,b,c from t1 where c='b' or c='a') NULL select ROW(1, 1, 'a') IN (select b,a,c from t1 where c='b' or c='a'); ROW(1, 1, 'a') IN (select b,a,c from t1 where c='b' or c='a') 1 select ROW(1, 1, 'a') IN (select b,a,c from t1 limit 2); ERROR 42000: This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery' drop table t1; create table t1 (a int); insert into t1 values (1); do @a:=(SELECT a from t1); select @a; @a 1 set @a:=2; set @a:=(SELECT a from t1); select @a; @a 1 drop table t1; do (SELECT a from t1); ERROR 42S02: Table 'test.t1' doesn't exist set @a:=(SELECT a from t1); ERROR 42S02: Table 'test.t1' doesn't exist CREATE TABLE t1 (a int, KEY(a)); HANDLER t1 OPEN; HANDLER t1 READ a=((SELECT 1)); ERROR 42000: You have an error in your SQL syntax. Check the manual that corresponds to your MySQL server version for the right syntax to use HANDLER t1 CLOSE; drop table t1; create table t1 (a int); create table t2 (b int); insert into t1 values (1),(2); insert into t2 values (1); select a from t1 where a in (select a from t1 where a in (select b from t2)); a 1 drop table t1, t2; create table t1 (a int, b int); create table t2 like t1; insert into t1 values (1,2),(1,3),(1,4),(1,5); insert into t2 values (1,2),(1,3); select * from t1 where row(a,b) in (select a,b from t2); a b 1 2 1 3 drop table t1, t2; CREATE TABLE `t1` (`i` int(11) NOT NULL default '0',PRIMARY KEY (`i`)) TYPE=MyISAM CHARSET=latin1; INSERT INTO t1 VALUES (1); UPDATE t1 SET i=i+1 WHERE i=(SELECT MAX(i)); ERROR HY000: Invalid use of group function drop table t1; CREATE TABLE t1 (a int(1)); EXPLAIN SELECT (SELECT RAND() FROM t1) FROM t1; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t1 system NULL NULL NULL NULL 0 const row not found 2 UNCACHEABLE SUBQUERY t1 system NULL NULL NULL NULL 0 const row not found EXPLAIN SELECT (SELECT ENCRYPT('test') FROM t1) FROM t1; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t1 system NULL NULL NULL NULL 0 const row not found 2 UNCACHEABLE SUBQUERY t1 system NULL NULL NULL NULL 0 const row not found EXPLAIN SELECT (SELECT BENCHMARK(1,1) FROM t1) FROM t1; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t1 system NULL NULL NULL NULL 0 const row not found 2 UNCACHEABLE SUBQUERY t1 system NULL NULL NULL NULL 0 const row not found drop table t1; CREATE TABLE `t1` ( `mot` varchar(30) character set latin1 NOT NULL default '', `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 (`mot`,`pseudo`,`date`,`topic`), KEY `pseudo` (`pseudo`,`date`,`topic`), KEY `topic` (`topic`) ) TYPE=MyISAM CHARSET=latin1 ROW_FORMAT=DYNAMIC; CREATE TABLE `t2` ( `mot` varchar(30) character set latin1 NOT NULL default '', `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 (`mot`,`pseudo`,`date`,`topic`), KEY `pseudo` (`pseudo`,`date`,`topic`), KEY `topic` (`topic`) ) TYPE=MyISAM CHARSET=latin1 ROW_FORMAT=DYNAMIC; CREATE TABLE `t3` ( `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 CHARSET=latin1; INSERT INTO t1 VALUES ('joce','1','','joce'),('test','2','','test'); Warnings: Warning 1263 Data truncated for column 'date' at row 1 Warning 1263 Data truncated for column 'date' at row 2 INSERT INTO t2 VALUES ('joce','1','','joce'),('test','2','','test'); Warnings: Warning 1263 Data truncated for column 'date' at row 1 Warning 1263 Data truncated for column 'date' at row 2 INSERT INTO t3 VALUES (1,1); SELECT DISTINCT topic FROM t2 WHERE NOT EXISTS(SELECT * FROM t3 WHERE numeropost=topic); topic 2 select * from t1; mot topic date pseudo joce 1 0000-00-00 joce test 2 0000-00-00 test DELETE FROM t1 WHERE topic IN (SELECT DISTINCT topic FROM t2 WHERE NOT EXISTS(SELECT * FROM t3 WHERE numeropost=topic)); select * from t1; mot topic date pseudo joce 1 0000-00-00 joce drop table t1, t2, t3; SELECT * FROM (SELECT 1 as a,(SELECT a)) a; a (SELECT a) 1 1 CREATE TABLE t1 SELECT * FROM (SELECT 1 as a,(SELECT 1)) a; SHOW CREATE TABLE t1; Table Create Table t1 CREATE TABLE `t1` ( `a` bigint(1) NOT NULL default '0', `(SELECT 1)` bigint(1) NOT NULL default '0' ) TYPE=MyISAM CHARSET=latin1 drop table t1; CREATE TABLE t1 SELECT * FROM (SELECT 1 as a,(SELECT a)) a; SHOW CREATE TABLE t1; Table Create Table t1 CREATE TABLE `t1` ( `a` bigint(1) NOT NULL default '0', `(SELECT a)` bigint(1) NOT NULL default '0' ) TYPE=MyISAM CHARSET=latin1 drop table t1; CREATE TABLE t1 SELECT * FROM (SELECT 1 as a,(SELECT a+0)) a; SHOW CREATE TABLE t1; Table Create Table t1 CREATE TABLE `t1` ( `a` bigint(1) NOT NULL default '0', `(SELECT a+0)` bigint(17) NOT NULL default '0' ) TYPE=MyISAM CHARSET=latin1 drop table t1; CREATE TABLE t1 SELECT (SELECT 1 as a UNION SELECT 1+1 limit 1,1) as a; SHOW CREATE TABLE t1; Table Create Table t1 CREATE TABLE `t1` ( `a` bigint(1) NOT NULL default '0' ) TYPE=MyISAM CHARSET=latin1 drop table t1; create table t1 (a int); insert into t1 values (1), (2), (3); explain select a,(select (select rand() from t1 limit 1) from t1 limit 1) from t1; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t1 ALL NULL NULL NULL NULL 3 2 UNCACHEABLE SUBQUERY t1 ALL NULL NULL NULL NULL 3 3 UNCACHEABLE SUBQUERY t1 ALL NULL NULL NULL NULL 3 drop table t1; select t1.Continent, t2.Name, t2.Population from t1 LEFT JOIN t2 ON t1.Code = t2.Country where t2.Population IN (select max(t2.Population) AS Population from t2, t1 where t2.Country = t1.Code group by Continent); ERROR 42S02: Table 'test.t1' doesn't exist CREATE TABLE t1 ( ID int(11) NOT NULL auto_increment, name char(35) NOT NULL default '', t2 char(3) NOT NULL default '', District char(20) NOT NULL default '', Population int(11) NOT NULL default '0', PRIMARY KEY (ID) ) TYPE=MyISAM; INSERT INTO t1 VALUES (130,'Sydney','AUS','New South Wales',3276207); INSERT INTO t1 VALUES (131,'Melbourne','AUS','Victoria',2865329); INSERT INTO t1 VALUES (132,'Brisbane','AUS','Queensland',1291117); CREATE TABLE t2 ( Code char(3) NOT NULL default '', Name char(52) NOT NULL default '', Continent enum('Asia','Europe','North America','Africa','Oceania','Antarctica','South America') NOT NULL default 'Asia', Region char(26) NOT NULL default '', SurfaceArea float(10,2) NOT NULL default '0.00', IndepYear smallint(6) default NULL, Population int(11) NOT NULL default '0', LifeExpectancy float(3,1) default NULL, GNP float(10,2) default NULL, GNPOld float(10,2) default NULL, LocalName char(45) NOT NULL default '', GovernmentForm char(45) NOT NULL default '', HeadOfState char(60) default NULL, Capital int(11) default NULL, Code2 char(2) NOT NULL default '', PRIMARY KEY (Code) ) TYPE=MyISAM; INSERT INTO t2 VALUES ('AUS','Australia','Oceania','Australia and New Zealand',7741220.00,1901,18886000,79.8,351182.00,392911.00,'Australia','Constitutional Monarchy, Federation','Elisabeth II',135,'AU'); INSERT INTO t2 VALUES ('AZE','Azerbaijan','Asia','Middle East',86600.00,1991,7734000,62.9,4127.00,4100.00,'Az�rbaycan','Federal Republic','Heyd�r �liyev',144,'AZ'); select t2.Continent, t1.Name, t1.Population from t2 LEFT JOIN t1 ON t2.Code = t1.t2 where t1.Population IN (select max(t1.Population) AS Population from t1, t2 where t1.t2 = t2.Code group by Continent); Continent Name Population Oceania Sydney 3276207 drop table t1, t2; CREATE TABLE `t1` ( `id` mediumint(8) unsigned NOT NULL auto_increment, `pseudo` varchar(35) character set latin1 NOT NULL default '', PRIMARY KEY (`id`), UNIQUE KEY `pseudo` (`pseudo`), ) TYPE=MyISAM PACK_KEYS=1 ROW_FORMAT=DYNAMIC; INSERT INTO t1 (pseudo) VALUES ('test'); SELECT 0 IN (SELECT 1 FROM t1 a); 0 IN (SELECT 1 FROM t1 a) 0 EXPLAIN SELECT 0 IN (SELECT 1 FROM t1 a); id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY NULL NULL NULL NULL NULL NULL NULL No tables used 2 DEPENDENT SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables INSERT INTO t1 (pseudo) VALUES ('test1'); SELECT 0 IN (SELECT 1 FROM t1 a); 0 IN (SELECT 1 FROM t1 a) 0 EXPLAIN SELECT 0 IN (SELECT 1 FROM t1 a); id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY NULL NULL NULL NULL NULL NULL NULL No tables used 2 DEPENDENT SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables drop table t1; CREATE TABLE `t1` ( `i` int(11) NOT NULL default '0', PRIMARY KEY (`i`) ) TYPE=MyISAM CHARSET=latin1; INSERT INTO t1 VALUES (1); UPDATE t1 SET i=i+(SELECT MAX(i) FROM (SELECT 1) t) WHERE i=(SELECT MAX(i)); ERROR HY000: Invalid use of group function UPDATE t1 SET i=i+1 WHERE i=(SELECT MAX(i)); ERROR HY000: Invalid use of group function UPDATE t1 SET t.i=i+(SELECT MAX(i) FROM (SELECT 1) t); ERROR 42S02: Unknown table 't' in field list drop table t1; CREATE TABLE t1 ( id int(11) default NULL ) TYPE=MyISAM CHARSET=latin1; INSERT INTO t1 VALUES (1),(1),(2),(2),(1),(3); CREATE TABLE t2 ( id int(11) default NULL, name varchar(15) default NULL ) TYPE=MyISAM CHARSET=latin1; INSERT INTO t2 VALUES (4,'vita'), (1,'vita'), (2,'vita'), (1,'vita'); update t1, t2 set t2.name='lenka' where t2.id in (select id from t1); select * from t2; id name 4 vita 1 lenka 2 lenka 1 lenka drop table t1,t2; create table t1 (a int, unique index indexa (a)); insert into t1 values (-1), (-4), (-2), (NULL); select -10 IN (select a from t1 FORCE INDEX (indexa)); -10 IN (select a from t1 FORCE INDEX (indexa)) NULL drop table t1; create table t1 (id int not null auto_increment primary key, salary int, key(salary)); insert into t1 (salary) values (100),(1000),(10000),(10),(500),(5000),(50000); explain SELECT id FROM t1 where salary = (SELECT MAX(salary) FROM t1); id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t1 ref salary salary 5 const 1 Using where 2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Select tables optimized away drop table t1; CREATE TABLE t1 ( ID int(10) unsigned NOT NULL auto_increment, SUB_ID int(3) unsigned NOT NULL default '0', REF_ID int(10) unsigned default NULL, REF_SUB int(3) unsigned default '0', PRIMARY KEY (ID,SUB_ID), UNIQUE KEY t1_PK (ID,SUB_ID), KEY t1_FK (REF_ID,REF_SUB), KEY t1_REFID (REF_ID) ) TYPE=MyISAM CHARSET=cp1251; INSERT INTO t1 VALUES (1,0,NULL,NULL),(2,0,NULL,NULL); SELECT DISTINCT REF_ID FROM t1 WHERE ID= (SELECT DISTINCT REF_ID FROM t1 WHERE ID=2); REF_ID DROP TABLE t1; create table t1 (a int, b int); create table t2 (a int, b int); insert into t1 values (1,0), (2,0), (3,0); insert into t2 values (1,1), (2,1), (3,1), (2,2); update ignore t1 set b=(select b from t2 where t1.a=t2.a); Warnings: Error 1240 Subselect returns more than 1 record select * from t1; a b 1 1 2 NULL 3 1 drop table t1, t2; create table t1(City VARCHAR(30),Location geometry); insert into t1 values("Paris",GeomFromText('POINT(2.33 48.87)')); select City from t1 where (select intersects(GeomFromText(AsText(Location)),GeomFromText('Polygon((2 50, 2.5 50, 2.5 47, 2 47, 2 50))'))=0); City drop table t1; CREATE TABLE `t1` ( `id` mediumint(8) unsigned NOT NULL auto_increment, `pseudo` varchar(35) NOT NULL default '', `email` varchar(60) NOT NULL default '', PRIMARY KEY (`id`), UNIQUE KEY `email` (`email`), UNIQUE KEY `pseudo` (`pseudo`), ) TYPE=MyISAM CHARSET=latin1 PACK_KEYS=1 ROW_FORMAT=DYNAMIC; INSERT INTO t1 (id,pseudo,email) VALUES (1,'test','test'),(2,'test1','test1'); SELECT pseudo as a, pseudo as b FROM t1 GROUP BY (SELECT a) ORDER BY (SELECT id*1); a b test test test1 test1 drop table if exists t1; (SELECT 1 as a) UNION (SELECT 1) ORDER BY (SELECT a+0); a 1 CREATE TABLE t1 ( FOLDERID VARCHAR(32)BINARY NOT NULL , FOLDERNAME VARCHAR(255)BINARY NOT NULL , CREATOR VARCHAR(255)BINARY , CREATED TIMESTAMP NOT NULL , DESCRIPTION VARCHAR(255)BINARY , FOLDERTYPE INTEGER NOT NULL , MODIFIED TIMESTAMP , MODIFIER VARCHAR(255)BINARY , FOLDERSIZE INTEGER NOT NULL , PARENTID VARCHAR(32)BINARY , REPID VARCHAR(32)BINARY , ORIGINATOR INTEGER , PRIMARY KEY ( FOLDERID ) ) TYPE=InnoDB; CREATE INDEX FFOLDERID_IDX ON t1 (FOLDERID); CREATE INDEX CMFLDRPARNT_IDX ON t1 (PARENTID); INSERT INTO t1 VALUES("0c9aab05b15048c59bc35c8461507deb", "System", "System", "2003-06-05 16:30:00", "The system content repository folder.", "3", "2003-06-05 16:30:00", "System", "0", NULL, "9c9aab05b15048c59bc35c8461507deb", "1"); INSERT INTO t1 VALUES("2f6161e879db43c1a5b82c21ddc49089", "Default", "System", "2003-06-09 10:52:02", "The default content repository folder.", "3", "2003-06-05 16:30:00", "System", "0", NULL, "03eea05112b845949f3fd03278b5fe43", "1"); INSERT INTO t1 VALUES("c373e9f5ad0791724315444553544200", "AddDocumentTest", "admin", "2003-06-09 10:51:25", "Movie Reviews", "0", "2003-06-09 10:51:25", "admin", "0", "2f6161e879db43c1a5b82c21ddc49089", "03eea05112b845949f3fd03278b5fe43", NULL); SELECT 'c373e9f5ad0791a0dab5444553544200' IN(SELECT t1.FOLDERID FROM t1 WHERE t1.PARENTID='2f6161e879db43c1a5b82c21ddc49089' AND t1.FOLDERNAME = 'Level1'); 'c373e9f5ad0791a0dab5444553544200' IN(SELECT t1.FOLDERID FROM t1 WHERE t1.PARENTID='2f6161e879db43c1a5b82c21ddc49089' AND t1.FOLDERNAME = 'Level1') 0 drop table t1;