1、创建组合查询
使用union把多条select语句的结果组成一个结果集。
例子
方法一：
select cust_name, cust_contact, cust_email
from customers
where cust_state in ('IL','IN','MI')
union
select cust_name, cust_contact, cust_email
from customers
where cust_name = 'Fun4All';
方法二：
select cust_name, cust_contact, cust_email
from customers
where cust_state in ('IL','IN','MI')
or cust_name = 'Fun4All';
/*
cust_name, cust_contact, cust_email
Village Toys John Smith sales@villagetoys.com
Fun4All Jim Jones jjones@fun4all.com
The Toy Store Kim Howard
Fun4All Denise L. Stephens dstephens@fun4all.com
*/
2、对组合结果排序
在最后一个select语句的最后使用order by，则结果集可以排序输出。
select cust_name, cust_contact, cust_email
from customers
where cust_state in ('IL','IN','MI')
union
select cust_name, cust_contact, cust_email
from customers
where cust_name = 'Fun4All'
order by cust_name, cust_contact;
/*
cust_name, cust_contact, cust_email
Fun4All Denise L. Stephens dstephens@fun4all.com
Fun4All Jim Jones jjones@fun4all.com
The Toy Store Kim Howard
Village Toys John Smith sales@villagetoys.com
*/