SQL HAVING 子句

HAVING 子句

在 SQL 中增加 HAVING 子句原因是，WHERE 关键字无法与合计函数一起使用。

--group by 和having 解释：前提必须了解sql语言中一种特殊的函数：聚合函数

SQL HAVING 语法

SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name
HAVING aggregate_function(column_name) operator value

SQL HAVING 实例

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

现在，我们希望查找订单总金额少于 2000 的客户。

我们使用如下 SQL 语句：

SELECT Customer,SUM(OrderPrice) FROM Orders
GROUP BY Customer
HAVING SUM(OrderPrice)<2000

结果集类似：

Customer	SUM(OrderPrice)
Carter	1700

现在我们希望查找客户 "Bush" 或 "Adams" 拥有超过 1500 的订单总金额。

我们在 SQL 语句中增加了一个普通的 WHERE 子句：

SELECT Customer,SUM(OrderPrice) FROM Orders
WHERE Customer='Bush' OR Customer='Adams'
GROUP BY Customer
HAVING SUM(OrderPrice)>1500

结果集：

Customer	SUM(OrderPrice)
Bush	2000
Adams	2000