Oracle 多表关联更新

drop table course;
create table course (
id integer,
teacherNo integer,
teacherDesc varchar2(100),
teacherName varchar2(50),
courseName varchar2(50)
);
insert into course values(1,100,‘Mr.zhang‘,‘ZhangSan‘,‘English‘);
insert into course values(2,101,‘Mr.wang‘,‘WangWu‘,‘History‘);
insert into course values(2,101,‘Mr.wang‘,‘WangWu‘,‘Chinese‘);

update course set teacherDesc=‘Good Teacher‘ where teacherNo=101;
commit;
drop table teacher;
create table teacher(
id integer,
teacherDesc varchar2(100),
teacherName varchar2(50)
);
insert into teacher values(100,‘Mr.zhang‘,‘ZhangSan‘);
insert into teacher values(101,‘Mr.wang‘,‘WangWu‘);
update teacher set teacherDesc=‘Excellent Teacher‘ where id=101;
commit;
select c.teacherdesc, c.teachername, t.teacherdesc, t.teachername
  from course c, teacher t
 where c.teacherno = t.id
   and (c.teacherdesc != t.teacherdesc or c.teachername != t.teachername);


update course c
   set (c.teacherdesc, c.teachername) =
       (select t.teacherdesc, t.teachername
          from teacher t
         where c.teacherno = t.id
           and (c.teacherdesc != t.teacherdesc or
               c.teachername != t.teachername))
 where exists (select 1
          from teacher t
         where c.teacherno = t.id
           and (c.teacherdesc != t.teacherdesc or
               c.teachername != t.teachername));
commit;
select c.teacherdesc, c.teachername, t.teacherdesc, t.teachername
  from course c, teacher t
 where c.teacherno = t.id
   and (c.teacherdesc != t.teacherdesc or c.teachername != t.teachername);

select c.teacherdesc, c.teachername, t.teacherdesc, t.teachername
  from course c, teacher t
 where c.teacherno = t.id;