带顶部和分组依据的SQL Server查询

Question

Given a table of the following structure:

subscriber_id,band

11,1

12,1

13,1

...

21,2

22,2

23,2

24,2

...

n1,n

n2,n

n3,n

...

nm,n

I want to get a subgroup of n% size of the subscribers from each group. For 10%, I should get 10% of group 1, 10% of group 2... 10% of group n.

Answer 1

It sounds like you want a stratified sample. You can get this by first enumerating within each group and then choosing the "n" records you want. Here is an example of how to do this in SQL Server:

select t.id, t.band
from (select t.*,
             row_number() over (order by band_seqnum) as seqnum
      from (select t.*,
                   row_number() over (partition by band order by rand(checksum()) as band_seqnum,
                   count(*) over () as cnt
            from t
           ) t
     ) t
where band_seqnum <= 0.10 * cnt;

Answer 2

Try This

Select * from 
(
Select *, NTILE(n%) over(partition by id order by id) 'R' from t)t
where t.R<=(n%)