含站点变化的公交车座位计算动态算法

Question

鉴于下面的数据库结果，

• BusStopNumber 中的空值表示摩加迪沙的 Origin
• BusStopNumber2 中的空值表示在这种情况下内罗毕的目的地

如果巴士上共有 10 个座位。

当乘客想要从摩加迪沙前往哈尔格萨（目的地之前的最后一站）并且我们从初始点到最终点预订了 2 个座位时，计算剩余座位数的最佳方法是什么？同样，我想从 SeatsCount 列计算可用座位，该列表示所有路线的预订座位数。

Answer 1

declare @booking table
(
    id int identity,
    busid int,
    scheduleid int,
    stopnumber smallint,
    stopnumber2 smallint,
    seatscount smallint
);

insert into @booking(busid, scheduleid, stopnumber, stopnumber2, seatscount)
values 
(1, 6, null, null, 2),
(1, 6, null, 1, 2),
(1, 6, null, 2, 1),
(1, 6, null, 3, 2),
(1, 6, 1, null, 2),
(1, 6, 1, 2, 1),
(1, 6, 1, 3, 1),
(1, 6, 2, null, 1),
(1, 6, 2, 3, 1),
(1, 6, 3, null, 2);

select * from @booking;


select *, 
--total number of passengers that got on the bus at previous&current stops
(select isnull(sum(e.seatscount), 0) from @booking as e where e.busid = b.busid and e.scheduleid = b.scheduleid and isnull(e.stopnumber, 0) <= isnull(b.stopnumber, 0))
-
--total number of passengers that got off the bus at previous&current stops
(select isnull(sum(d.seatscount), 0) from @booking as d where d.busid = b.busid and d.scheduleid = b.scheduleid and d.stopnumber2 <= b.stopnumber)
as PassengersOnBusAtStopNumber
from @booking as b;