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;