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