理解join- -

author:zfive5(zhaozidong)
email:[e-mail]

不说只看

a or b
select a.AId,b.BId from U1A a left join U1B b on a.AId=b.BId
union
select a.AId,b.BId from U1A a right join U1B b on a.AId=b.BId

a or b
select a.AId,b.BId from U1A a full join U1B b on a.AId=b.BId

a and b
select a.AId,b.BId from U1A a inner join U1B b on a.AId=b.BId

a
select a.AId,b.BId from U1A a left join U1B b on a.AId=b.BId

b
select a.AId,b.BId from U1A a right join U1B b on a.AId=b.BId

a*b
select a.AId,b.BId from U1A a right join U1B b on a.AId=b.BId

OK！