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;
Unknown column 'a' in 'field list'
SELECT 1 as a FROM (SELECT a UNION SELECT 1) b;
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;
Unknown column 'a' in 'having clause'
SELECT a,b as a FROM (SELECT '1' as a,'2' as b) b  HAVING a=1;
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;
Unknown column 'a' in 'where clause'
SELECT (SELECT 1) as a FROM (SELECT 1 FROM t1  HAVING a=1) as a;
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	<derived2>	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	<derived2>	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	<derived2>	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
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	index	NULL	a	4	NULL	10000	Using index
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;
Unknown column 'a' in 'field list'
SELECT 1 as a FROM (SELECT a UNION SELECT 1) b;
Unknown column 'a' in 'field list'
SELECT 1 as a FROM (SELECT 1 UNION SELECT a) b;
Unknown column 'a' in 'field list'
select 1 from  (select 2) a order by 0;
Unknown column '0' in 'order clause'