SQL用先进先出存储过程求出库数量

 create table t(
 id int identity(1,1), name varchar(50),--商品名称
 j int,        --入库数量
 c int,        --出库数量
 jdate datetime --入库时间
 )
 insert into t(name,j,c,jdate) select  'A',100,0,'2007-12-01'
 insert into t(name,j,c,jdate) select  'A',200,0,'2008-01-07'
 insert into t(name,j,c,jdate) select  'B',320,0,'2007-12-21'
 insert into t(name,j,c,jdate) select  'A',100,0,'2008-01-15'
 insert into t(name,j,c,jdate) select  'B',90,0,'2008-02-03'
 insert into t(name,j,c,jdate) select  'A',460,0,'2008-02-01'
 insert into t(name,j,c,jdate) select  'A',510,0,'2008-03-01'
 go

create proc wsp
@name varchar(50),--商品名称
@cost int         --销售量
as
--先得出该货物的库存是否够
declare @spare float --剩余库存
select @spare=sum(j)-sum(c) from t where name=@name
if(@spare>=@cost)
   begin
    --根据入库日期采用先进先出原则对货物的库存进行处理
     update t set c=
     case when (select @cost-isnull(sum(j),0)+isnull(sum(c),0) from t where name=@name and jdate<=a.jdate and j!=c)>=0
     then a.j
     else
        case when (select @cost-isnull(sum(j),0)+isnull(sum(c),0) from t where name=@name and jdate<a.jdate and j!=c)<0
        then 0
        else (select @cost-isnull(sum(j),0)+isnull(sum(c),0)+a.c from t where name=@name and jdate<a.jdate and j!=c)
        end
     end
     from t a where name=@name and j!=c
   end
else
    raiserror('库存不足',16,1)
    return
go

exec wsp @name='A',@cost=100