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。

语法：
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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

例子1：查找订单总金额少于 2000 的客户

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

例子2：查找客户 "Bush" 或 "Adams" 拥有超过 1500 的订单总金额

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

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