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 global 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;
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
drop table if exists t1,t2;
CREATE TABLE t1 (  id int(3) unsigned default '0') TYPE=MyISAM;
INSERT INTO t1 (id) VALUES("1");
CREATE TABLE t2 ( id int(3) unsigned default '0',  id_master int(5) default '0',  text1 varchar(5) default NULL,  text2 varchar(5) default NULL) TYPE=MyISAM;
INSERT INTO t2 (id, id_master, text1, text2) VALUES("1", "1",
"foo1", "bar1");
INSERT INTO t2 (id, id_master, text1, text2) VALUES("2", "1",
"foo2", "bar2");
INSERT INTO t2 (id, id_master, text1, text2) VALUES("3", "1", NULL,
"bar3");
INSERT INTO t2 (id, id_master, text1, text2) VALUES("4", "1",
"foo4", "bar4");
SELECT 1 AS id_master, 1 AS id, NULL AS text1, 'ABCDE' AS text2 UNION SELECT id_master, t2.id, text1, text2 FROM t1 LEFT JOIN t2 ON t1.id = t2.id_master;
id_master	id	text1	text2
1	1	NULL	ABCDE
1	1		bar1
1	2		bar2
1	3	NULL	bar3
1	4		bar4
SELECT 1 AS id_master, 1 AS id, 'ABCDE' AS text1, 'ABCDE' AS text2 UNION SELECT id_master, t2.id, text1, text2 FROM t1 LEFT JOIN t2 ON t1.id = t2.id_master;
id_master	id	text1	text2
1	1	ABCDE	ABCDE
1	1	foo1	bar1
1	2	foo2	bar2
1	3	NULL	bar3
1	4	foo4	bar4
drop table if exists t1,t2;
(SELECT 1,3) UNION (SELECT 2,1) ORDER BY (SELECT 2);
1	3
1	3
2	1
create table t1 (a int not null primary key auto_increment, b int, key(b));
create table t2 (a int not null primary key auto_increment, b int);
insert into t1 (b) values (1),(2),(2),(3);
insert into t2 (b) values (10),(11),(12),(13);
explain (select * from t1 where a=1) union (select * from t2 where a=1);
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t1	const	PRIMARY	PRIMARY	4	const	1	
2	UNION	t2	const	PRIMARY	PRIMARY	4	const	1	
(select * from t1 where a=5) union (select * from t2 where a=1);
a	b
1	10
(select * from t1 where a=5 and a=6) union (select * from t2 where a=1);
a	b
1	10
(select t1.a,t1.b from t1,t2 where t1.a=5) union (select * from t2 where a=1);
a	b
1	10
(select * from t1 where a=1) union (select t1.a,t2.a from t1,t2 where t1.a=t2.a);
a	b
1	1
2	2
3	3
4	4
explain (select * from t1 where a=1 and b=10) union (select t1.a,t2.a from t1,t2 where t1.a=t2.a);
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
2	UNION	t1	index	PRIMARY	PRIMARY	4	NULL	4	Using index
2	UNION	t2	index	PRIMARY	PRIMARY	4	NULL	4	Using where; Using index
explain (select * from t1 where a=1) union (select * from t1 where b=1);
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t1	const	PRIMARY	PRIMARY	4	const	1	
2	UNION	t1	ref	b	b	5	const	1	Using where
drop table t1,t2;
(select 1) union (select 2) order by 0;
Unknown column '0' in 'order clause'
SELECT @a:=1 UNION SELECT @a:=@a+1;
@a:=1
1
2
(SELECT 1) UNION (SELECT 2) ORDER BY (SELECT a);
Unknown column 'a' in 'field list'