group by 在什么情况下使用?使用场景是什么
show databases;
create database c1;
use c1;
DROP TABLE CUS;
create table Cus(
ORDERID INT PRIMARY KEY auto_increment,
CUSNAME varchar (10),
PRODUCTNAME VARCHAR (10),
PRODUCTPRICE INT,
ORDERDATE date
);
DESC CUS;
INSERT INTO CUS VALUES
(3012,'A','P001',100,'2020-6-1'),
(3013,'B','P002',78,'2020-6-2'),
(3014,'C','P003',123,'2020-6-3'),
(3015,'A','P004',98,'2020-6-1'),
(3016,'B','P005',45,'2020-6-2'),
(3017,'C','P001',100,'2020-6-3'),
(3018,'A','P005',45,'2020-6-3'),
(3019,'B','P004',98,'2020-6-1');
select * from cus;
-- 统计6月1号,2号每个Customer购买的产品总价。
select CUSNAME,ORDERDATE,SUM(PRODUCTPRICE) as 产品总价
from cus
where ORDERDATE='2020-6-1' or ORDERDATE='2020-6-2'
group by CUSNAME;
订单表是事实表,产品表和品牌是维度表,一事实多维度难道不是星型模式吗?品牌不能与订单表相连,那不就剩一个订单表链接产品表了?那不是交叉吗?