oracle：聯表更新多個欄位的值

兩個表有某些欄位對應，然後分別更新。

就寫了下面的sql用於測試。

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drop table a;
drop table b;
create table a(a1 number,a2 number,a3 number, id number);
create table b(b1 number,b2 number,b3 number, id number);
insert into a values(10,10,10,1);
insert into a values(20,20,20,2);
insert into a values(30,30,30,3);
insert into a values(40,40,40,4);

insert into b values(1,1,1,1);
insert into b values(2,2,2,2);
insert into b values(3,3,3,3);
insert into b values(4,4,4,4);

commit;

update a
set (a1,a2,a3)=(select a1-b1,a2-b2,a3-b3 from b where b.id=a.id)
where exists(select 1 from b where b.id=a.id);

commit;