Question

我有一个查询，该查询获得了比赛中跑步者开始比赛时间的最早日期：

SELECT
    MIN(races.eventdate)
FROM
    races,
    runners
WHERE
    races.id=runners.raceid AND runners.time_hsecs IS NOT NULL

races表有一个种族列表，以及它们所在的轨道。 runners表包含每个种族及其时间的跑步者。

上面的查询获取记录完成时间的最早日期。但是，如果我想获得每个曲目名称的最早日期呢？凭借我有限的经验，我将创建一个循环，遍历每个曲目名称，然后执行上面相同的查询，但仅隔离到每个曲目，例如（伪代码）

foreach($trackname_array as $some_name) {

    SELECT
        MIN(races.eventdate)
    FROM
        races,
        runners
    WHERE
        races.id=runners.raceid AND runners.time_hsecs IS NOT NULL
    AND
        races.trackname=$some_name

    // returns earliest eventdate that matches the query for trackname

}

但我想了解这样的事情是如何完全在sql中完成的？

Answer 1

您似乎在寻找GROUP BY语法：

SELECT
    MIN(races.eventdate) as eventDate, races.id AS raceId,races.trackname
 FROM
    races,
    runners
WHERE
    races.id=runners.raceid AND runners.time_hsecs IS NOT NULL
GROUP BY races.id, races.trackName

Answer 2

SELECT
    MIN(races.eventdate) as eventDate,races.trackname
 FROM
    races,
    runners
WHERE
    races.id=runners.raceid AND runners.time_hsecs IS NOT NULL
GROUP BY  races.trackName, date(races.eventdate)

如果我理解正确

如何只用一个查询执行这个php循环和多个mysql查询？

2 个答案: