mysql聚合函数

常用的聚合函数有：

平均值：avg()

取个数：count()

取总和：sum()

取最大值：max()

取最小值：min()

用法：select  聚合函数 from 表名 group by 字段名;

例如：

select * from student;

select count(ssex) from student group by ssex;

select count(ssex) as a from student group by ssex having a>3;