--联接 select from dbo.k_baoming inner join dbo.k_kebiao on dbo.k_baoming.o_flowid = dbo.k_kebiao.f_apply_id --左向外联接 select dbo.k_baoming.o_flowid from dbo.k_baoming left outer join dbo.k_kebiao on dbo.k_baoming.o_flowid = dbo.k_kebia
--联接
select
from dbo.k_baoming inner join
      dbo.k_kebiao on dbo.k_baoming.o_flowid = dbo.k_kebiao.f_apply_id
--左向外联接
select dbo.k_baoming.o_flowid
from dbo.k_baoming left outer join
      dbo.k_kebiao on dbo.k_baoming.o_flowid = dbo.k_kebiao.f_kebiaoid
--右向外联接
select dbo.k_baoming.o_flowid
from dbo.k_baoming right outer join
      dbo.k_kebiao on dbo.k_baoming.o_flowid = dbo.k_kebiao.f_kebiaoid
--完整外部联接
select dbo.k_baoming.o_flowid
from dbo.k_baoming full outer join
      dbo.k_kebiao on dbo.k_baoming.o_flowid = dbo.k_kebiao.f_kebiaoid
--可以不要outer
--exists 与 in 互换
select * from article where classid in(select id from class where parentid='219')
go
select * from article where exists(select id from class where class.id=article.classid and class.parentid='219')
in适合于外表大而内表小的情况；exists适合于外表小而内表大的情况。