plsql的写法

求一个plsql的写法
id money rate 
1 100 100/400
2 300 300/400
3 350 1-100/400-300/400

计算rate：除了最后一条记录外，rate=money/400,最后一条记录的rate=1-（前面所有的rate和）。

------解决方案--------------------
如果id是1，2，3顺序排列的话就这样取
select id,money,money/400 rate from t where id<=(select count(*)-1 from t)
union
select id,money,1-(select sum(rate) from (select id,money,money/400 rate from t where id<=(select count(*)-1 from t))
 ) from t
------解决方案--------------------
修改表中的值
update t a set rate=(select money/400 from t b where a.id=b.id)
update t set rate=(select 1-sum(rate) from t where rownum<(select count(id) from t)) where id=(select max(id) from t)
------解决方案--------------------
修改下：

探讨

如果id是1，2，3顺序排列的话就这样取
select id,money,money/400 rate from t where id <=(select count(*)-1 from t)
union
select max(id) id,money,1-(select sum(rate) from (select id,money,money/400 rate from t where id <=(select count(*)-1 from t)) rate
) from t