declare @a table(a int,b int) declare @b table(a int,b int) insert @a values(1,1) insert @a values(2,2) insert @b values(1,1) insert @b values(3,3)--左: select * from @a Aa left join @b Bb on Aa.a=Bb.a --右: select * from @a Aa right join @b Bb on Aa.a=Bb.a --内 select * from @a Aa join @b Bb on Aa.a=Bb.a --外 select * from @a Aa full join @b Bb on Aa.a=Bb.a --完全 select * from @a,@b
select a.username,a.userage,b.usrname,b.recvmess from userinfo full join recvemss on a.username = b.username
LEFT OUTER JOIN RecvMess b ON a.UserName=b.UserName
select a.UserName,a.UserAge,b.RecvMess from UserInfo a
LEFT OUTER JOIN RecvMess b ON a.UserName=b.UserName
from UserInfo AS a LEFT JOIN RecvMess AS b ON a.UserName=b.UserName
from UserAge as a,RecvMess as b
where a.UserName*=b.UserName
from userinfo full join recvemss
on a.username = b.username
听完解释马上结题,大家再帮帮忙啊
declare @b table(a int,b int)
insert @a values(1,1)
insert @a values(2,2)
insert @b values(1,1)
insert @b values(3,3)--左:
select * from @a Aa left join @b Bb on Aa.a=Bb.a
--右:
select * from @a Aa right join @b Bb on Aa.a=Bb.a
--内
select * from @a Aa join @b Bb on Aa.a=Bb.a
--外
select * from @a Aa full join @b Bb on Aa.a=Bb.a
--完全
select * from @a,@b
from userinfo full join recvemss
on a.username = b.username