union

create table Websites

(

id int,

name varchar(50),

url varchar(500),

alexa float,

contry varchar(50)

)

delete from Websites

insert into Websites(id,name,url,alexa,contry)values(1,'Goole','www.baidu.com',1,'USA')

insert into Websites(id,name,url,alexa,contry)values(2,'淘宝','www.taobao.com',13,'CN')

insert into Websites(id,name,url,alexa,contry)values(3,'菜鸟教程','www.runnoob.com',4689,'CN')

insert into Websites(id,name,url,alexa,contry)values(4,'微博','www.weibo.com',20,'CN')

insert into Websites(id,name,url,alexa,contry)values(4,'facebook','www.facewook.com',3,'USA')

insert into Websites(id,name,url,alexa,contry)values(4,'STACKOVERFLOW','www.STACKOVERFLOW.com',3,'IND')

create table apps

(

  id int,

  appname varchar(50),

  url varchar(50),

  contry varchar(50)

)

insert into apps(id,appname,url,contry)values(1,'QQ app','http：//im.qq.com','CN')

insert into apps(id,appname,url,contry)values(2,'微博 app','http：//im.WEIBO.com','CN')

insert into apps(id,appname,url,contry)values(3,'淘宝 app','http：//im.TAOBOA.com','CN')

select * from apps

select * from Websites

select contry from Websites

union

select contry from apps

--查询出不同的值

select contry from Websites

union all

select contry from apps

--where条件

select contry from Websites where contry='CN'

union all

select contry from apps where contry='CN'

order by contry

sql UNION 操作符

sql union用于合并两个或者多个select语句结果集。

sql union 语法

select * from table1

union

select * from table2

默认的，union操作符操作不同的值，如果允许有重复的值，请使用union all.