Mysql中的Order by和Group by

一：Order by 排序

示例：表 s

1.默认为升序

select * from s order by age

2.升序：ASC

同上

3.降序：DESC

select * from s order by age desc

注：当排列中含有空值时

            ASC：排序列为空值的元组最后显示。

            DESC：排序列为空值的元组最先显示。

二：Group by 分组

1.聚合函数

select sex,avg(age) from s group by sex

2.Having

select sex,avg(age) from s group by sex having sex = '女'