求一个简单的触发器

[pgdoryoku]

平台:mssql2000
条件:1、已知有两表,表A和表B
2、表A中有字段，A1，A2
3、表B中有字段，B1，B2
问题:当更新表A中的A2字段的同时，更新表B中所有B2字段中的B2=A2的所有字段为新的A2。
要求：要有该触发器要有容错功能，且在建立之前会判断是否有同名触发器存在，有的话则删除同名的触发器在建立触发器。

[dawugui]

create trigger my_trig on A for update
as
  update b set b2 = a.a2 from b,a where b.b1 = a.a1

[中国风]

create trigger tr_A on A
for update
as
update B
set B2=i.A2
from
inserted i join deleted d on i.A1=D.A1
join B on B2=d.A2

[中国风]

如果是唯一的情况下建级联更新A的A2上

[wzy_love_sly]

create table a(a1 int,a2 int)
insert into a select 1,1
insert into a select 2,2


create table b(b1 int,b2 int)
insert into b select 1,1
insert into b select 2,1
insert into b select 3,2
insert into b select 4,2
insert into b select 5,2

create trigger tr_a
on a
for update
as
begin
update a set b2=b.a2 from b a,deleted c,inserted b
where a.b2=c.a2 and c.a1=b.a1
end

update a set a2=5 where a1=1

select * from a

select * from b

--a
a1	a2
1	5
2	2
--b
b1	b2
1	5
2	5
3	2
4	2
5	2

[pgdoryoku]

谢谢，在问下2楼的语句中
inserted i join deleted d on i.A1=D.A1
这句什么意思？

[中国风]

deleted 和 inserted 是逻辑（概念）表

--一个是更新前，一个是更新后状态

[中国风]

inserted i join deleted d on i.A1=D.A1
这句什么意思？

inserted --别名为i表
deleted --别名为d表

[sun9moon]

create table a(a1 int,a2 int)
insert into a select 1,1
insert into a select 2,2

create table b(b1 char(1),b2 int)
insert into b select 'a',1
insert into b select 'b',1
insert into b select 'c',2
insert into b select 'd',2
insert into b select 'e',2
go
if exists(select 1 from sysobjects where name ='ut_a_update' and type='tr')
drop trigger ut_a_update
go
create trigger ut_a_update on a for update
as
update b set b2=i.a2
from inserted i join deleted d on i.a1=d.A1
join b on b.b2=d.a2
go
--测试
select * from b
update a set a2=3 where a2=1
select * from b

drop table a
drop table b
go