HAVING：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。
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 |
原文：http://www.cnblogs.com/wuqiuxue/p/7677072.html