sql UNION ALL用法详解

union all 这个指令的目的也是要将两个 sql 语句的结果合并在一起。 union all 和 union 不同之处在于 union all 会将每一笔符合条件的资料都列出来，无论资料值有无重复。

union all 的语法如下：

[sql 语句 1]
union all
[sql 语句 2]

我们用和上一页同样的例子来显示出 union all 和 union 的不同。同样假设我们有以下两个表格，

1> create table employee(
2> id int,
3> name nvarchar (10),
4> salary int,
5> start_date datetime,
6> city nvarchar (10),
7> region char (1))
8> go
1>
2> insert into employee (id, name, salary, start_date, city, region)
3> values (1, 'jason', 40420, '02/01/94', 'new york', 'w')
4> go

(1 rows affected)
1> insert into employee (id, name, salary, start_date, city, region)
2> values (2, 'robert',14420, '01/02/95', 'vancouver','n')
3> go

(1 rows affected)
1> insert into employee (id, name, salary, start_date, city, region)
2> values (3, 'celia', 24020, '12/03/96', 'toronto', 'w')
3> go

(1 rows affected)
1> insert into employee (id, name, salary, start_date, city, region)
2> values (4, 'linda', 40620, '11/04/97', 'new york', 'n')
3> go

(1 rows affected)
1> insert into employee (id, name, salary, start_date, city, region)
2> values (5, 'david', 80026, '10/05/98', 'vancouver','w')
3> go

(1 rows affected)
1> insert into employee (id, name, salary, start_date, city, region)
2> values (6, 'james', 70060, '09/06/99', 'toronto', 'n')
3> go

(1 rows affected)
1> insert into employee (id, name, salary, start_date, city, region)
2> values (7, 'alison',90620, '08/07/00', 'new york', 'w')
3> go

(1 rows affected)
1> insert into employee (id, name, salary, start_date, city, region)
2> values (8, 'chris', 26020, '07/08/01', 'vancouver','n')
3> go

(1 rows affected)
1> insert into employee (id, name, salary, start_date, city, region)
2> values (9, 'mary', 60020, '06/09/02', 'toronto', 'w')
3> go

(1 rows affected)
1>
2> * from employee
3> go
id name salary start_date city region
----------- ---------- ----------- ----------------------- ---------- ------
1 jason 40420 1994-02-01 00:00:00.000 new york w
2 robert 14420 1995-01-02 00:00:00.000 vancouver n
3 celia 24020 1996-12-03 00:00:00.000 toronto w
4 linda 40620 1997-11-04 00:00:00.000 new york n
5 david 80026 1998-10-05 00:00:00.000 vancouver w
6 james 70060 1999-09-06 00:00:00.000 toronto n
7 alison 90620 2000-08-07 00:00:00.000 new york w
8 chris 26020 2001-07-08 00:00:00.000 vancouver n
9 mary 60020 2002-06-09 00:00:00.000 toronto w

(9 rows affected)
1>
2>
3> select id, name from employee where name like 'c%'
4> union all
5> select id, name from employee where name like 'a%'
6> go
id name
----------- ----------
3 celia
8 chris
7 alison

(3 rows affected)
1>
2> drop table employee
3> go
1>