SQL查询：仅在查询中包含行的PAIRS

Question

Im looking to find pairs of rows in a table like below

MS SQL 2012(maybe 2014)

Ref, Split
1, A
1, B
2, B
3, A
3, B

Results

Ref, Split
1, A
1, B
3, A
3, B

pairs of rows are partitioned by 'Ref' ie, 1 and 3 need to be returned, but 2 does not have a pair so should not be returned

I would by default use OVER but i believe this is overkill and not the most effective way of handling this.

What are the alternatives

Answer 1

Why not use a self-join and put the results in one row?

select t1.ref, t1.split, t2.split
from t t1 join 
     t t2
     on t1.ref = t2.ref;

Or if you want the original rows use exists :

select t.*
from t
where exists (select 1 from t t2 where t2.ref = t.ref and t2.split <> t.split);

Answer 2

If your DBMS supports count() over() it's just the way to go.

select t.Ref, t.Split
from (
   select Ref, Split, count(distinct Split) over(partition by Ref) cnt
) t
where t.cnt > 1 
-- cnt = 2  if exactly the pairs are required