select * from [left]  l
where not exists (
select * from [right] r
where l.name=r.name
)
结果为50条
-----------------------------
--下面这个例子充分说明,not exists不能单单理解为差集
select * from [right]  r
where not exists (
select * from [left] l
where l.name=r.name
)
结果为空集