having()闲谈

在sql中使用group 分组以后还想对结果进行筛选的话，就需要用到having（）

例1：

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2：

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

可见having后面一般都是聚合函数的筛选，别的筛选条件在前面的where语句中and连用就好

当然，having后面也可以用and或者or连用条件

例3：

select count(f_fund_id),count(f2) from table_name group by f_fund_id ,f2 having count(f_fund_id)>1 and count(f2)>3

 

所以可以理解为，where是在进行group by前的筛选，而having()就是对group by 后的又一次筛选