if object_id('[a]') is not null drop table [a]
create table a
(
    [id] int not null IDENTITY(1,1),
    age int
)

if object_id('[b]') is not null drop table [b]
create table b
(
    [id] int not null IDENTITY(1,1),
    age datetime
)

insert into a (age) values (12)
insert into b (age) values ('2000-01-01')
go 
Select * From a
Select * From b
/*目的：用约束的方式实现当b表age字段修改时相应的更新a表的age字段。
      比如2001-01-01改成1999-01-01则a表age应该变成13*/

 /*这个约束能实现吗？ 还是用触发器吧*/
 create trigger tr_b_update on b
 for update
 as
 begin
     
     update a set age = d.age
     from a s inner join 
     (select id ,datediff(year,age,getdate()) as age from inserted) d on s.id = d.id
            
 end

------解决方案--------------------
写个触发器的，约束好像实现不了
SQL code
create trigger tri_b_upd
on b
for update
as
if update(age)
begin
  update a set age=datediff(yy,i.age,getdate())
  from inserted i
  where a.id=i.id
end
go

update b set age='1999-01-01' where id=1
go

select * from a
/**
id          age
----------- -----------
1           13

(1 行受影响)
**/

------解决方案--------------------
SQL code

CREATE Trigger tr_b_update
on b
for update
as
if update(age)
begin
  update a 
          set age=datediff(year,x.age,getdate())
          from inserted x  
          where a.id=x.id
end
go