对于预订系统,有一个库存表,每个项目都有一个数量(例如,有 20 张椅子)。现在,用户可以预订特定时间段(例如,两小时 5 张椅子“2010-11-23 15:00”-“2010-11-23 17:00”;另一次预订可以持续几天“2010-11-24 11:00”-“2010-11-26 14:00”)。
检查在请求的时间段内仍有多少商品可用的最佳方法是什么?
用户应该输入他想要预订的时间(从,到),并且他应该看到在此期间仍有多少库存商品。
table "inventory"
-------------------
inventory_id (int)
quantity (int)
table "reservation"
-------------------
reservation_id (int)
inventory_id (int)
quantity (int)
from (datetime)
until (datetime)
预留可以重叠,但对于某个时间点,仅应预留库存.数量 项。
简单示例:
我们有 40 张椅子。
存在以下保留:
R1 2010-11-23 14:00 - 2010-11-23 15:30 -> 5 chairs reserved
R2 2010-11-23 15:00 - 2010-11-23 16:00 -> 10 chairs reserved
R3 2010-11-23 17:00 - 2010-11-23 17:30 -> 20 chairs reserved
用户提出多个预订请求(查询):
Q1 2010-11-23 15:00 - 2010-11-23 17:00 -> 25 chairs are available
Q2 2010-11-23 15:45 - 2010-11-23 17:00 -> 30 chairs are available
Q3 2010-11-23 16:30 - 2010-11-23 18:00 -> 30 chairs are available
Q4 2010-11-23 15:10 - 2010-11-23 15:20 -> 25 chairs are available
Q5 2010-11-23 13:30 - 2010-11-23 17:30 -> 20 chairs are available
如何查询请求期间的最大可用数量?或者是否需要不同的 table 设计?目标数据库系统是Oracle和SQL-Server。
更新:
我尝试在不更改原始示例的情况下“可视化”保留 R1 和 R2 以及查询 Q1 - Q5。我添加了 Q4 和 Q5 作为附加示例。 av 显示可用数量。
R1 R2 R3 av
13:30 40 Q5
14:00 5 35 Q5
14:30 5 35 Q5
15:00 5 10 25 Q1 Q5
15:10 5 10 25 Q1 Q4 Q5
15:20 5 10 25 Q1 Q5
15:30 10 30 Q1 Q5
15:45 10 30 Q1 Q2 Q5
16:00 40 Q1 Q2 Q5
16:30 40 Q1 Q2 Q3 Q5
17:00 20 20 Q3 Q5
av 25 30 20 25 20
最佳答案
你可以尝试这样的事情(完整的工作示例)
DECLARE @inventory TABLE(
inventory_id int,
quantity int
)
DECLARE @reservation TABLE(
reservation_id int,
inventory_id int,
quantity int,
[from] datetime,
until datetime
)
INSERT INTO @inventory SELECT 1, 40
INSERT INTO @reservation SELECT 1, 1, 5, '2010-11-23 14:00 ', '2010-11-23 15:30'
INSERT INTO @reservation SELECT 1, 1, 10, '2010-11-23 15:00 ', '2010-11-23 16:00'
DECLARE @Start DATETIME,
@End DATETIME
SELECT @Start = '2010-11-23 15:00',
@End = '2010-11-23 17:00'
SELECT TotalUsed.inventory_id,
i.quantity - ISNULL(TotalUsed.TotalUsed,0) Available
FROM @inventory i LEFT JOIN
(
SELECT inventory_id,
SUM(quantity) TotalUsed
FROM @reservation
WHERE [from] BETWEEN @Start AND @End
OR until BETWEEN @Start AND @End
GROUP BY inventory_id
) TotalUsed ON TotalUsed.inventory_id = i.inventory_id
SELECT @Start = '2010-11-23 15:45',
@End = '2010-11-23 17:00'
SELECT TotalUsed.inventory_id,
i.quantity - ISNULL(TotalUsed.TotalUsed,0) Available
FROM @inventory i LEFT JOIN
(
SELECT inventory_id,
SUM(quantity) TotalUsed
FROM @reservation
WHERE [from] BETWEEN @Start AND @End
OR until BETWEEN @Start AND @End
GROUP BY inventory_id
) TotalUsed ON TotalUsed.inventory_id = i.inventory_id
结果
inventory_id Available
------------ -----------
1 25
inventory_id Available
------------ -----------
1 30
关于SQL查询特定时间段内最大可用商品数(预订系统),我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/3433727/