含义
where
在分组之前就进行选择操作
having
having在分组操作之后才进行选择操作，所以having可以选择聚合函数
eg：
|
1
2
3
4
|
// 下面这句是可以的
SELECT COUNT(*) FROM A
WHERE A.a1>0
GROUP BY a2；
|
|
1
2
3
4
|
//但是下面就不行
SELECT COUNT(*) FROM A
WHERE A.a1>0 and count(*)>1
GROUP BY a2；
|
|
1
2
3
4
5
|
//必须要改为having
SELECT COUNT(*) FROM A
WHERE A.a1>0
GROUP BY a2
HAVING COUNT(*)>1
|