Question

SQLserver中如何选取每一类的前三列

例如：
a b
1 mmm
2 mmm
3 mmm
4 mmm
1 nnn
2 nnn
3 nnn
我想得到的结果是
1 mmm
2 mmm
3 mmm
1 nnn
2 nnn
3 nnn

Answer 1

select top 3 a,b from
(select * , ROW_NUMBER()over(order by b,a) as c
from table1)aa where b='mmm'
union all
select top 3 a,b from
(select * , ROW_NUMBER()over(order by b,a) as c
from table1)aa where b='nnn'

Answer 2

关注一下

Answer 3

select top 3 a,b
from table_name
group by b;