drop table if exists t1,t2;
select 1, 1.0, -1, "hello", NULL;
Catalog	Database	Table	Table_alias	Column	Column_alias	Name	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
def					1	8	1	1	N	32769	0	8
def					1.0	5	3	3	N	32769	1	8
def					-1	8	1	2	N	32769	0	8
def					hello	254	5	5	N	1	31	8
def					NULL	6	0	0	Y	32768	0	8
1	1.0	-1	hello	NULL
1	1.0	-1	hello	NULL
create table t1 (a tinyint, b smallint, c mediumint, d int, e bigint, f float(3,2), g double(4,3), h decimal(5,4), i year, j date, k timestamp, l datetime, m enum('a','b'), n set('a','b'), o char(10));
select * from t1;
Catalog	Database	Table	Table_alias	Column	Column_alias	Name	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
def	test	t1	t1	a	a	1	4	0	Y	32768	0	63
def	test	t1	t1	b	b	2	6	0	Y	32768	0	63
def	test	t1	t1	c	c	9	9	0	Y	32768	0	63
def	test	t1	t1	d	d	3	11	0	Y	32768	0	63
def	test	t1	t1	e	e	8	20	0	Y	32768	0	63
def	test	t1	t1	f	f	4	3	0	Y	32768	2	63
def	test	t1	t1	g	g	5	4	0	Y	32768	3	63
def	test	t1	t1	h	h	0	7	0	Y	32768	4	63
def	test	t1	t1	i	i	13	4	0	Y	32864	0	63
def	test	t1	t1	j	j	10	10	0	Y	128	0	63
def	test	t1	t1	k	k	7	19	0	N	1249	0	63
def	test	t1	t1	l	l	12	19	0	Y	128	0	63
def	test	t1	t1	m	m	254	1	0	Y	256	0	8
def	test	t1	t1	n	n	254	3	0	Y	2048	0	8
def	test	t1	t1	o	o	254	10	0	Y	0	0	8
a	b	c	d	e	f	g	h	i	j	k	l	m	n	o
select a b, b c from t1 as t2;
Catalog	Database	Table	Table_alias	Column	Column_alias	Name	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
def	test	t1	t2	a	b	1	4	0	Y	32768	0	63
def	test	t1	t2	b	c	2	6	0	Y	32768	0	63
b	c
drop table t1;
CREATE TABLE t1 (id tinyint(3) default NULL, data varchar(255) default NULL);
INSERT INTO t1 VALUES (1,'male'),(2,'female');
CREATE TABLE t2 (id tinyint(3) unsigned default NULL, data char(3) default '0');
INSERT INTO t2 VALUES (1,'yes'),(2,'no');
select t1.id, t1.data, t2.data from t1, t2 where t1.id = t2.id;
Catalog	Database	Table	Table_alias	Column	Column_alias	Name	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
def	test	t1	t1	id	id	1	3	1	Y	32768	0	63
def	test	t1	t1	data	data	253	255	6	Y	0	0	8
def	test	t2	t2	data	data	254	3	3	Y	0	0	8
id	data	data
1	male	yes
2	female	no
select t1.id, t1.data, t2.data from t1, t2 where t1.id = t2.id order by t1.id;
Catalog	Database	Table	Table_alias	Column	Column_alias	Name	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
def	test	t1	t1	id	id	1	3	1	Y	32768	0	63
def	test	t1	t1	data	data	253	255	6	Y	0	0	8
def	test	t2	t2	data	data	254	3	3	Y	0	0	8
id	data	data
1	male	yes
2	female	no
select t1.id from t1 union select t2.id from t2;
Catalog	Database	Table	Table_alias	Column	Column_alias	Name	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
def	test	t1	t1	id	id	1	3	1	Y	32768	0	63
id
1
2
drop table t1,t2;