drop table if exists t1,t2,t3; select * from (select 2 from DUAL) b; 2 2 SELECT 1 as a FROM (SELECT 1 UNION SELECT a) b; ERROR 42S22: Unknown column 'a' in 'field list' SELECT 1 as a FROM (SELECT a UNION SELECT 1) b; ERROR 42S22: Unknown column 'a' in 'field list' CREATE TABLE t1 (a int not null, b char (10) not null); insert into t1 values(1,'a'),(2,'b'),(3,'c'),(3,'c'); CREATE TABLE t2 (a int not null, b char (10) not null); insert into t2 values (3,'c'),(4,'d'),(5,'f'),(6,'e'); select t1.a,t3.y from t1,(select a as y from t2 where b='c') as t3 where t1.a = t3.y; a y 3 3 3 3 select t1.a,t3.a from t1,(select * from t2 where b='c') as t3 where t1.a = t3.a; a a 3 3 3 3 CREATE TABLE t3 (a int not null, b char (10) not null); insert into t3 values (3,'f'),(4,'y'),(5,'z'),(6,'c'); select t1.a,t4.y from t1,(select t2.a as y from t2,(select t3.b from t3 where t3.a>3) as t5 where t2.b=t5.b) as t4 where t1.a = t4.y; a y 3 3 3 3 SELECT a FROM (SELECT 1 FROM (SELECT 1) a HAVING a=1) b; ERROR 42S22: Unknown column 'a' in 'having clause' SELECT a,b as a FROM (SELECT '1' as a,'2' as b) b HAVING a=1; ERROR 23000: Column: 'a' in having clause is ambiguous SELECT a,2 as a FROM (SELECT '1' as a) b HAVING a=2; a a 1 2 SELECT a,2 as a FROM (SELECT '1' as a) b HAVING a=1; a a SELECT 1 FROM (SELECT 1) a WHERE a=2; ERROR 42S22: Unknown column 'a' in 'where clause' SELECT (SELECT 1) as a FROM (SELECT 1 FROM t1 HAVING a=1) as a; ERROR 42S22: Unknown column 'a' in 'having clause' select * from t1 as x1, (select * from t1) as x2; a b a b 1 a 1 a 2 b 1 a 3 c 1 a 3 c 1 a 1 a 2 b 2 b 2 b 3 c 2 b 3 c 2 b 1 a 3 c 2 b 3 c 3 c 3 c 3 c 3 c 1 a 3 c 2 b 3 c 3 c 3 c 3 c 3 c explain select * from t1 as x1, (select * from t1) as x2; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY x1 ALL NULL NULL NULL NULL 4 1 PRIMARY ALL NULL NULL NULL NULL 4 2 DERIVED x1 ALL NULL NULL NULL NULL 4 drop table if exists t2,t3; select * from (select 1) as a; 1 1 select a from (select 1 as a) as b; a 1 select 1 from (select 1) as a; 1 1 select * from (select * from t1 union select * from t1) a; a b 1 a 2 b 3 c select * from (select * from t1 union all select * from t1) a; a b 1 a 2 b 3 c 3 c 1 a 2 b 3 c 3 c explain select * from (select * from t1 union select * from t1) a; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY ALL NULL NULL NULL NULL 3 2 DERIVED t1 ALL NULL NULL NULL NULL 4 3 UNION t1 ALL NULL NULL NULL NULL 4 explain select * from (select * from t1 union all select * from t1) a; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY ALL NULL NULL NULL NULL 8 2 DERIVED t1 ALL NULL NULL NULL NULL 4 3 UNION t1 ALL NULL NULL NULL NULL 4 CREATE TABLE t2 (a int not null); insert into t2 values(1); select * from (select * from t1 where t1.a=(select a from t2 where t2.a=t1.a)) a; a b 1 a select * from (select * from t1 where t1.a=(select t2.a from t2 where t2.a=t1.a) union select t1.a, t1.b from t1) a; a b 1 a 2 b 3 c explain select * from (select * from t1,t2 where t1.a=t2.a) t1; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY system NULL NULL NULL NULL 1 2 DERIVED t2 system NULL NULL NULL NULL 1 2 DERIVED t1 ALL NULL NULL NULL NULL 4 Using where drop table t1, t2; create table t1(a int not null, t char(8), index(a)); SELECT * FROM (SELECT * FROM t1) as b ORDER BY a ASC LIMIT 0,20; a t 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 explain select count(*) from t1 as tt1, (select * from t1) as tt2; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Select tables optimized away 2 DERIVED tt1 ALL NULL NULL NULL NULL 10000 drop table t1; SELECT * FROM (SELECT (SELECT * FROM (SELECT 1 as a) as a )) as b; (SELECT * FROM (SELECT 1 as a) as a ) 1 select * from (select 1 as a) b left join (select 2 as a) c using(a); a a 1 NULL SELECT * FROM (SELECT 1 UNION SELECT a) b; ERROR 42S22: Unknown column 'a' in 'field list' SELECT 1 as a FROM (SELECT a UNION SELECT 1) b; ERROR 42S22: Unknown column 'a' in 'field list' SELECT 1 as a FROM (SELECT 1 UNION SELECT a) b; ERROR 42S22: Unknown column 'a' in 'field list' select 1 from (select 2) a order by 0; ERROR 42S22: Unknown column '0' in 'order clause' create table t1 (id int); insert into t1 values (1),(2),(3); describe select * from (select * from t1 group by id) bar; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY ALL NULL NULL NULL NULL 3 2 DERIVED t1 ALL NULL NULL NULL NULL 3 Using temporary; Using filesort drop table t1; create table t1 (mat_id MEDIUMINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY, matintnum CHAR(6) NOT NULL, test MEDIUMINT UNSIGNED NULL); create table t2 (mat_id MEDIUMINT UNSIGNED NOT NULL, pla_id MEDIUMINT UNSIGNED NOT NULL); insert into t1 values (NULL, 'a', 1), (NULL, 'b', 2), (NULL, 'c', 3), (NULL, 'd', 4), (NULL, 'e', 5), (NULL, 'f', 6), (NULL, 'g', 7), (NULL, 'h', 8), (NULL, 'i', 9); insert into t2 values (1, 100), (1, 101), (1, 102), (2, 100), (2, 103), (2, 104), (3, 101), (3, 102), (3, 105); SELECT d.pla_id, m2.mat_id FROM t1 m2 INNER JOIN (SELECT mp.pla_id, MIN(m1.matintnum) AS matintnum FROM t2 mp INNER JOIN t1 m1 ON mp.mat_id=m1.mat_id GROUP BY mp.pla_id) d ON d.matintnum=m2.matintnum; pla_id mat_id 100 1 101 1 102 1 103 2 104 2 105 3 SELECT d.pla_id, m2.test FROM t1 m2 INNER JOIN (SELECT mp.pla_id, MIN(m1.matintnum) AS matintnum FROM t2 mp INNER JOIN t1 m1 ON mp.mat_id=m1.mat_id GROUP BY mp.pla_id) d ON d.matintnum=m2.matintnum; pla_id test 100 1 101 1 102 1 103 2 104 2 105 3 explain SELECT d.pla_id, m2.mat_id FROM t1 m2 INNER JOIN (SELECT mp.pla_id, MIN(m1.matintnum) AS matintnum FROM t2 mp INNER JOIN t1 m1 ON mp.mat_id=m1.mat_id GROUP BY mp.pla_id) d ON d.matintnum=m2.matintnum; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY m2 ALL NULL NULL NULL NULL 9 1 PRIMARY ALL NULL NULL NULL NULL 6 Using where 2 DERIVED mp ALL NULL NULL NULL NULL 9 Using temporary; Using filesort 2 DERIVED m2 index NULL PRIMARY 3 NULL 9 Using index explain SELECT d.pla_id, m2.test FROM t1 m2 INNER JOIN (SELECT mp.pla_id, MIN(m1.matintnum) AS matintnum FROM t2 mp INNER JOIN t1 m1 ON mp.mat_id=m1.mat_id GROUP BY mp.pla_id) d ON d.matintnum=m2.matintnum; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY m2 ALL NULL NULL NULL NULL 9 1 PRIMARY ALL NULL NULL NULL NULL 6 Using where 2 DERIVED mp ALL NULL NULL NULL NULL 9 Using temporary; Using filesort 2 DERIVED m2 index NULL PRIMARY 3 NULL 9 Using index drop table t1,t2; SELECT a.x FROM (SELECT 1 AS x) AS a HAVING a.x = 1; x 1 create table a1 select 1 as a; select 2 as a from (select * from a1) b; ERROR 3D000: No Database Selected use test; select 2 as a from (select * from a1) b; a 2 drop table a1;