分组和筛选

select

from

where

grouo by分组

having分组在筛选

order by排序

select shb ，count(*)

from zx_student

where (xb='nan')

group by shb 按照班级分组

having count(*) > 50 分组进行筛选

order by 2

select *

from zx_student

where xm in (

select xm

from zx_student

group by xm

having count(*) > 1)

order by xm