十万火急!!!请问这个sql怎么写?

[icw_zy]

create table a ( id int, ch char(1));
create table b ( id int, ch char(1));

insert into a(1, '1');
insert into a(2, '2');

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

现在我需要根据b的id字段修改a的ch字段

就是把a中的内容改为:(1, '3') (2, '4')

[zjhclf]

update a set ch =(select ch from b where a.id=id)

[tiangou]

以下语句在8i上运行通过
========================================================
SQL> select * from a;

ID SM
---------- ------------------------------
1 bad1
2 bad1
3 bad1

SQL> select * from b;

ID SM
---------- ------------------------------
1 good1
2 good2
3 good3

SQL> update a set a.sm = (select b.sm from b where a.id = b.id and rownum<=1);

3 rows updated

SQL> select * from a;

ID SM
---------- ------------------------------
1 good1
2 good2
3 good3

SQL> select * from b;

ID SM
---------- ------------------------------
1 good1
2 good2
3 good3

SQL>

[lvxinsi]

同意楼上两位的回答

[icw_zy]

不好意思,刚才我看错了,你们说的方法是对的,谢谢