关于sql的update的问题

[willianzhong]

我现在有两个表
费用(feiyong) 字段 kh(卡号) fy (费用)
计费(jifei) 字段 kh (卡号) jf (计费)
现在主表 feiyong 外表jifei 两者已经建了关联
现在要修改费用表,把费用表中的 费用 fy- 计费表的计费jf
怎么写sql来修改费用表中的字段fy?
下面出错了
update feiyong set fy=fy-feiyong.jf
where feiyong.ka=jifei.kh

请问怎么写

[willianzhong]

刚才搞错了
update feiyong set fy=fy-jifei.jf
where feiyong.ka=jifei.kh

[weiwenking]

update feiyong set fy=fy-(select jf from jifei where kh=feiyong.kh)
这里没有考虑jifei的相应记录不存在,若为NULL应另加处理

[yown]

update feiyong a set fy=fy-NVL(t2.jf,0)

where exists (select 1 from feiyong t1,jifei t2 where t1.kh=t2.kh )

[baojianjun]

樓上的可以

[chenchen2003]

UPDATE feiyong SET fy=fy-(SELECT NVL(jf) FROM jifei WHERE kh=feiyong.kh)

[chenchen2003]

上面错了。不好意思。
UPDATE feiyong SET fy=fy-(SELECT NVL(jf,0) FROM jifei WHERE kh=feiyong.kh)

[yearlist]

update feiyong a set fy=( select fee
from
(　select t1.kh kh,t1.fy-t2.jf fee
　from feiyong t1,jifei t2
　where t1.kh=t2.kh
)b where a.kh=b.kh
　　　)
where exists (select 1 from feiyong t1,jifei t2 where t1.kh=t2.kh )

[yearlist]

我写的比较复杂，不过肯定对。如果表中数据有null值，注意使用decode()函数进行过滤。