GROUP BY 语句用于结合合计函数，根据一个或多个列对结果集进行分组

 1 drop table orders;
 2 create table orders (
 3 o_id int auto_increment primary key,
 4 orderdate date,
 5 orderprice int,
 6 customer varchar(100)
 7 );
 8
 9 insert into orders(orderdate, orderprice, customer) values('2008-12-29', 1000, 'Bush');
10 insert into orders(orderdate, orderprice, customer) values('2008-11-23', 1600, 'Carter');
11 insert into orders(orderdate, orderprice, customer) values('2008-10-05', 700, 'Bush');
12 insert into orders(orderdate, orderprice, customer) values('2008-09-28', 300, 'Bush');
13 insert into orders(orderdate, orderprice, customer) values('2008-08-06', 2000, 'Adams');
14 insert into orders(orderdate, orderprice, customer) values('2008-07-21', 100, 'Carter');
15
16 select * from orders;
17
18 SELECT customer,SUM(orderprice) FROM orders
19 GROUP BY customer;

我们拥有下面这个 "Orders" 表：

O_Id	OrderDate	OrderPrice	Customer
1	2008/12/29	1000	Bush
2	2008/11/23	1600	Carter
3	2008/10/05	700	Bush
4	2008/09/28	300	Bush
5	2008/08/06	2000	Adams
6	2008/07/21	100	Carter

我们使用下列 SQL 语句：

SELECT Customer,SUM(OrderPrice) FROM Orders
GROUP BY Customer

结果集类似这样：

Customer	SUM(OrderPrice)
Bush	2000
Carter	1700
Adams	2000