至少 只有
at least 
only
这两种条件用什么实现呢？

------解决方案--------------------
至少有一条的
select id ,name from tab
where name='a'
group by id
having count(name)>1
------解决方案--------------------

探讨

select * from a where (select count(*) from b where a.i=b.i)=1;
select * from a where (select count(*) from b where a.i=b.i)>0;

这样写可以吗