select a,b from tb group by a,b having count(*)>1

------解决方案--------------------
SQL code
if object_id('[tb]') is not null drop table [tb]
go
create table [tb]([A] int,[B] int)
insert [tb]
select 1,1 union all
select 1,2 union all
select 2,3 union all
select 2,3 union all
select 2,4 union all
select 3,5 union all
select 3,5 union all
select 3,5 union all
select 3,6
go

;with cte as
(select rn=row_number() over(order by getdate()),* from tb)

select a.a,a.b
from cte a
join (select min(rn) as rn,a,b from cte group by a,b) b
on a.a=b.a and a.b=b.b and a.rn!=b.rn

/**
a           b
----------- -----------
2           3
3           5
3           5

(3 行受影响)
**/