同意楼上
select A from [tableName] group by A having count(1) > 1

------解决方案--------------------
楼上正解
A,B字段没有重复的吧?

------解决方案--------------------
SQL code
create table tb(A int ,  B  varchar(10))
insert into tb select 1,  'a' 
insert into tb select 2 , 'b' 
insert into tb select 2 , 'c' 
insert into tb select 3 , 'd'
insert into tb select 4 , 'd' 
insert into tb select 5 , 'd' 
insert into tb select 5 , 'c' 

select * from tb where a in (select A from tb group by A having count(b) > 1)

------解决方案--------------------
select * from t
where A in (select A from t group by A having count(1)>1)