select * from TableB a where not exists(select 1 from TableB where ParentID = a.ParentID and id<a.id)

------解决方案--------------------
探讨


引用:
select * from TableB a where id = (select top 1 id from TableB where a.ParentID = ParentID)



可是TableB的某些字段需要作为查询条件呀,而且TableB的一些字段也需要展示出来


------解决方案--------------------
SQL code

create table TableA(id int)

insert into TableA
select 1 union all
select 2 union all
select 3

create table TableB(id int,ParentID int)

insert into TableB
select 1, 1 union all
select 2, 2 union all
select 3, 2 union all
select 4, 3 union all
select 5, 3 union all
select 6, 3


select a.id,b.id 'ParentID'
from TableA a
inner join
(select row_number() over(partition by ParentID order by getdate()) rn,
id,ParentID from TableB) b
on a.id=b.ParentID and b.rn=1

id          ParentID
----------- -----------
1           1
2           2
3           4

(3 row(s) affected)