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我写了一个查询，允许我使用 groupwise max 方法获取最近的房间。但是我如何对多列进行分组最大值？

我有下面的查询，其中子查询为我提供了最近的房间，然后将它们与主表连接起来。现在我想选择接下来会发生的第一个事件。

例如：MIN(DATEDIFF(date, now())) > 0

SELECT name, date, t1.Room, descr, t1.D
FROM Events
JOIN
(
        SELECT Roomid, Room, Latitude, Longitude,
                ACOS(SIN((:lat))*SIN(RADIANS(Latitude)) + COS((:lat))*COS(RADIANS(Latitude))*COS(RADIANS(Longitude)-(:lon)))*(:R) AS D
        FROM Rooms
        WHERE Latitude>(:minLat) AND Latitude<(:maxLat)
                AND Longitude>(:minLon) AND Longitude<(:maxLon)
                AND ACOS(SIN((:lat))*SIN(RADIANS(Latitude)) + COS((:lat))*COS(RADIANS(Latitude))*COS(RADIANS(Longitude)-(:lon)))*(:R) < (:rad)
) AS t1 ON Events.roomid = t1.Roomid
GROUP BY Room
ORDER BY D

有人可以告诉我如何做到这一点吗？

谢谢！

PS：该事件应该是下一个发生的事件。我不使用 ABS(MIN()) 因为这将返回已经发生的事件。

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1 回答 1

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假设 D 是您的日期，按日期差排序并限制 1

SELECT name, date, t1.Room, descr, t1.D
FROM Events
JOIN
(
        SELECT Roomid, Room, Latitude, Longitude,
            ACOS(SIN((:lat))*SIN(RADIANS(Latitude)) + COS((:lat))*COS(RADIANS(Latitude))*COS(RADIANS(Longitude)-(:lon)))*(:R) AS D
    FROM Rooms
    WHERE Latitude>(:minLat) AND Latitude<(:maxLat)
            AND Longitude>(:minLon) AND Longitude<(:maxLon)
            AND ACOS(SIN((:lat))*SIN(RADIANS(Latitude)) + COS((:lat))*COS(RADIANS(Latitude))*COS(RADIANS(Longitude)-(:lon)))*(:R) < (:rad)
) AS t1 ON Events.roomid = t1.Roomid
ORDER BY DATEDIFF( D, now())
LIMIT 1
于 2012-03-23T00:32:02.543 回答