Question

请帮助MySQL新手：

我有2张桌子：

assets

asset_id |  description
------------------------
001      |  Crate of Laptops
002      |  Crate of OhBots
003      |  Crate of Spheros


bookings

id       | asset_id   |  start_date     |     end_date   |   location
----------------------------------------------------------------------
1        | 001        |    2018/10/01   |   2018/10/10   |   Barnet
2        | 001        |    2018/10/12   |   2018/10/15   |   Hendon
3        | 002        |    2018/10/01   |   2018/10/10   |   Finchley
4        | 001        |    2018/12/01   |   2018/12/04   |   Brent

我需要显示开始日期小于今天的每种资产的所有最新预订-因此，如果今天是2018/10/19，则应向我提供预订ID的详细信息：

asset_id     |       location
------------------------------
001          |       Hendon
002          |       Finchley

到目前为止，我有这个，但它不显示最新的预订-它显示所有的预订。我想我需要一个使用MAX（）的子查询，但无法正常工作。关于如何从表中获取最新值的文章很多，但我也需要过去的start_date。

SELECT asset.asset_id, asset.description, booking.location, booking.start_date
FROM  assets AS asset
INNER JOIN bookings AS booking 
ON asset.asset_id=booking.asset_id
WHERE booking.start_date <= NOW()
ORDER BY asset.asset_id DESC;

Answer 1

您是正确的，您需要使用MAX()查找子查询中每种资产的最大开始日期，然后需要将其重新连接到booking表中以查找其他资产相应的信息。

SELECT a.id, a.description, b.start_date, b.location
FROM assets a
INNER JOIN bookings b ON (a.id = b.asset_id)
INNER JOIN (
    SELECT b.asset_id, MAX(b.start_date) AS start_date
    FROM bookings b
    WHERE b.start_date < CURDATE()
    GROUP BY b.asset_id
) c ON (b.asset_id = c.asset_id AND b.start_date = c.start_date)

这是一个有效的数据库提琴：https://www.db-fiddle.com/f/mci3TkZpZxKcJckWNVHrBK/0

Answer 2

您可以在开始日期之前订购。试试这个，

SELECT asset.asset_id, asset.description, booking.location, booking.start_date
FROM  assets AS asset
INNER JOIN bookings AS booking 
ON asset.asset_id=booking.asset_id
WHERE booking.start_date <= NOW()
ORDER BY asset.asset_id,booking.start_date DESC;

mysql查找比今天小的最新记录

2 个答案: