SQL处理库存与销售，先进先出原则

--库存表
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),
@cost int--,--销售量
--@returns int output --该货物的库存是否够（不够：-1；够：1）
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


--测试：

exec wsp @name='A',@cost=390
select * from t

--删除测试环境
drop table t
drop proc wsp