sql 怎么得到group by 后每个组内数据的条数

Answer 1

select id, count(*)
from tab
group by id

count(*)就是你id组对应的条数

Answer 2

假如表 test 字段 a， b；按照a分组
select a,count(*) 条数
from test
group by a

Answer 3

group by xx
having count(*)>=n