1.having只能放在groupby之后对分组后的结果进行筛选
2.where后的条件表达式里不能使用聚合函数，having可以
student
举个例子：
select * from student where sex = 1 group by class
select * from student group by class having sex = 1
//第一个是对查询筛选后的结果进行分组
//第二个是对查询分组后的结果进行筛选
两个结果不同
1
2
3.SELECT DISTINCT
SELECT DISTINCT 列名称 FROM 表名称
查询不同列名称的值（去重复）
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1.having只能放在groupby之后对分组后的结果进行筛选2.where后的条件表达式里不能使用聚合函数，h...
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1.索引 group by where having order byhttps://blog....
本文标题：where,having,group by
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