表与表之间的更新问题

select 1,* from sysobjects

insert into A(a,b,c)

select y.* from B as y left join A as x on y.a=x.a where x.a is null

--用别名

update x set x.b=y.b,x.c=y.c from A as x join B as y on x.a=y.a

insert A(a,b,c) select * from B as y where not exists (select 1 from A where a=y.a)

update A set A.b=B.b,A.c=B.c from A join B on A.a=B.a

insert A(a,b,c) select * from B where not exists (select 1 from A where a=B.a)

update a set a.b.=b.b,a.c=b.c from a join b on a.a=b.a



insert a(a,b,c) select * from b where not exists (select 1 from a where a=b.a)