drop table if exists t1,t2,t3;
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 a,b from t1 union select a,b from t2;
a	b
1	a
2	b
3	c
4	d
5	f
6	e
select a,b from t1 union all select a,b from t2;
a	b
1	a
2	b
3	c
3	c
3	c
4	d
5	f
6	e
select a,b from t1 union all select a,b from t2 order by b;
a	b
1	a
2	b
3	c
3	c
3	c
4	d
6	e
5	f
select a,b from t1 union all select a,b from t2 union select 7,'g';
a	b
1	a
2	b
3	c
3	c
3	c
4	d
5	f
6	e
7	g
select 0,'#' union select a,b from t1 union all select a,b from t2 union select 7,'gg';
0	#
0	#
1	a
2	b
3	c
3	c
3	c
4	d
5	f
6	e
7	g
select a,b from t1 union select a,b from t1;
a	b
1	a
2	b
3	c
select 't1',b,count(*) from t1 group by b UNION select 't2',b,count(*) from t2 group by b;
t1	b	count(*)
t1	a	1
t1	b	1
t1	c	2
t2	c	1
t2	d	1
t2	e	1
t2	f	1
(select a,b from t1 limit 2)  union all (select a,b from t2 order by a) limit 4;
a	b
1	a
2	b
3	c
4	d
(select a,b from t1 limit 2)  union all (select a,b from t2 order by a limit 1);
a	b
1	a
2	b
3	c
(select a,b from t1 limit 2)  union all (select a,b from t2 order by a limit 1) order by b desc;
a	b
3	c
2	b
1	a
(select a,b from t1 limit 2)  union all (select a,b from t2 order by a limit 1) order by t1.b;
Table 't1' from one of SELECT's can not be used  in order clause
explain (select a,b from t1 limit 2)  union all (select a,b from t2 order by a limit 1) order by b desc;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	
2	UNION	t2	ALL	NULL	NULL	NULL	NULL	4	Using filesort
select found_rows();
FOUND_ROWS()
0
explain select a,b from t1 union all select a,b from t2;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	
2	UNION	t2	ALL	NULL	NULL	NULL	NULL	4	
explain select xx from t1 union select 1;
Unknown column 'xx' in 'field list'
explain select a,b from t1 union select 1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	
2	UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
explain select 1 union select a,b from t1 union select 1;
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	UNION	t1	ALL	NULL	NULL	NULL	NULL	4	
3	UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
explain select a,b from t1 union select 1 limit 0;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
2	UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
select a,b from t1 into outfile 'skr' union select a,b from t2;
Wrong usage of UNION and INTO
select a,b from t1 order by a union select a,b from t2;
Wrong usage of UNION and ORDER BY
insert into t3 select a from t1 order by a union select a from t2;
Wrong usage of UNION and ORDER BY
create table t3 select a,b from t1 union select a from t2;
The used SELECT statements have a different number of columns
select a,b from t1 union select a from t2;
The used SELECT statements have a different number of columns
select * from t1 union select a from t2;
The used SELECT statements have a different number of columns
select a from t1 union select * from t2;
The used SELECT statements have a different number of columns
select * from t1 union select SQL_BUFFER_RESULT * from t2;
Wrong usage/placement of 'SQL_BUFFER_RESULT'
create table t3 select a,b from t1 union all select a,b from t2;
insert into t3 select a,b from t1 union all select a,b from t2;
replace into t3 select a,b as c from t1 union all select a,b from t2;
drop table t1,t2,t3;
CREATE TABLE t1 (
`pseudo` char(35) NOT NULL default '',
`pseudo1` char(35) NOT NULL default '',
`same` tinyint(1) unsigned NOT NULL default '1',
PRIMARY KEY  (`pseudo1`),
KEY `pseudo` (`pseudo`)
) TYPE=MyISAM;
INSERT INTO t1 (pseudo,pseudo1,same) VALUES ('joce', 'testtt', 1),('joce', 'tsestset', 1),('dekad', 'joce', 1);
SELECT pseudo FROM t1 WHERE pseudo1='joce' UNION SELECT pseudo FROM t1 WHERE pseudo='joce';
pseudo
dekad
joce
SELECT pseudo1 FROM t1 WHERE pseudo1='joce' UNION SELECT pseudo1 FROM t1 WHERE pseudo='joce';
pseudo1
joce
testtt
tsestset
SELECT * FROM t1 WHERE pseudo1='joce' UNION SELECT * FROM t1 WHERE pseudo='joce' order by pseudo desc,pseudo1 desc;
pseudo	pseudo1	same
joce	tsestset	1
joce	testtt	1
dekad	joce	1
SELECT pseudo1 FROM t1 WHERE pseudo='joce' UNION SELECT pseudo FROM t1 WHERE pseudo1='joce';
pseudo1
testtt
tsestset
dekad
SELECT pseudo1 FROM t1 WHERE pseudo='joce' UNION ALL SELECT pseudo FROM t1 WHERE pseudo1='joce';
pseudo1
testtt
tsestset
dekad
SELECT pseudo1 FROM t1 WHERE pseudo='joce' UNION SELECT 1;
pseudo1
testtt
tsestset
1
drop table t1;
drop table if exists t1,t2;
create table t1 (a int);
create table t2 (a int);
insert into t1 values (1),(2),(3),(4),(5);
insert into t2 values (11),(12),(13),(14),(15);
(select * from t1 limit 2) union (select * from t2 limit 3) limit 4;
a
1
2
11
12
(select * from t1 limit 2) union (select * from t2 limit 3);
a
1
2
11
12
13
(select * from t1 limit 2) union (select * from t2 limit 20,3);
a
1
2
set SQL_SELECT_LIMIT=2;
(select * from t1 limit 1) union (select * from t2 limit 3);
a
1
11
set SQL_SELECT_LIMIT=DEFAULT;
drop table t1,t2;
select * union select 1;
No tables used
select 1 as a,(select a union select a);
a	(select a union select a)
1	1