使用order by和group by的MYSQL子查询

我有两张桌子，联赛和赛季

赛季有

league\u id，开始日期

我正试图抓住每个联赛的最新赛季。。然后按asc顺序按赛季开始日期排序结果

SELECT *
FROM leagues
JOIN (
  SELECT id as season_id, title as season_title, league_id, start_date
  FROM seasons
  ORDER BY start_date DESC) AS seasons
  ON leagues.id = seasons.league_id
ORDER BY seasons.start_date ASC;

这件事我已经做了一段时间了。。这种方法很有效，但却能为一个联赛创造多个赛季的记录

我发现了一个使用PHP的解决方案，但我希望只使用MYSQL

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非常感谢您的建议。

您需要在子查询中使用一个

MAX（）

聚合，以获取每个季节的最新

开始日期，并将其与
季节表连接起来

SELECT 
  /* Don't SELECT * in production code - 
     trim this to just the columns you actually need */
  leagues.*,
  seasons.*
FROM 
  /* Start with an inner join between seasons and leagues */
  leagues
  INNER JOIN seasons ON leagues.id = seasons.league_id
  INNER JOIN (
    /* Subquery gets leage_id and latest start date per league_id group */
    SELECT
      league_id,
      MAX(start_date) AS maxstart
    FROM seasons
    GROUP BY league_id
    /* joining back to seasons on both of those columns to return 
       the full season column data */
  ) maxseason 
    ON seasons.league_id = maxseason.league_id
       AND seasons.start_date = maxseason.startdate
ORDER BY seasons.start_date ASC

您需要在子查询中使用
MAX（）
聚合来获取每个季节的最新
start\u日期
，并将其与
seasures
表连接起来

SELECT 
  /* Don't SELECT * in production code - 
     trim this to just the columns you actually need */
  leagues.*,
  seasons.*
FROM 
  /* Start with an inner join between seasons and leagues */
  leagues
  INNER JOIN seasons ON leagues.id = seasons.league_id
  INNER JOIN (
    /* Subquery gets leage_id and latest start date per league_id group */
    SELECT
      league_id,
      MAX(start_date) AS maxstart
    FROM seasons
    GROUP BY league_id
    /* joining back to seasons on both of those columns to return 
       the full season column data */
  ) maxseason 
    ON seasons.league_id = maxseason.league_id
       AND seasons.start_date = maxseason.startdate
ORDER BY seasons.start_date ASC

您可以非常简单地执行此操作，而无需使用自联接进行子查询：

SELECT s1.*, l.*
FROM seasons s1
LEFT JOIN seasons s2
  ON s2.league_id = s1.league_id AND s2.start_date > s1.start_date
JOIN leagues l
  ON l.id = s1.league_id
WHERE s2.league_id IS NULL
ORDER BY s1.start_date

此方法的性能通常优于子查询。
您可以非常简单地执行此操作，而无需使用自联接进行子查询：

SELECT s1.*, l.*
FROM seasons s1
LEFT JOIN seasons s2
  ON s2.league_id = s1.league_id AND s2.start_date > s1.start_date
JOIN leagues l
  ON l.id = s1.league_id
WHERE s2.league_id IS NULL
ORDER BY s1.start_date

此方法通常优于子查询。
您还可以使用group by：

SELECT *
FROM seasons s1
JOIN
    (SELECT l.id as league_id, s.id as season_id, MAX(start_date) as max_start_date
    FROM leagues l
    JOIN seasons s ON l.id = s.league_id
    GROUP BY l.id, s.id) ls ON (ls.season_id = s1.id AND s1.start_date = ls.max_start_date)
ORDER BY s1.start_date ASC

您还可以通过以下方式使用组：

SELECT *
FROM seasons s1
JOIN
    (SELECT l.id as league_id, s.id as season_id, MAX(start_date) as max_start_date
    FROM leagues l
    JOIN seasons s ON l.id = s.league_id
    GROUP BY l.id, s.id) ls ON (ls.season_id = s1.id AND s1.start_date = ls.max_start_date)
ORDER BY s1.start_date ASC

我希望我没有弄错你的问题

我希望我没有弄错你的问题。
感谢你的快速回复，我去测试了一下，但是我在“on子句”中得到了一个错误未知的列“maxseasons.league\u id”。它只是一个不正确的别名
maxseasons
应该是
maxseasons
非常感谢您这非常好用。。刚刚还必须将maxseason.startdate更改为maxseason.MaxStart收到快速回复，我去测试了一下，但在“on子句”中得到了一个错误未知的列“maxseasons.league_id”，它只是一个不正确的别名
maxseasons
应该是
maxseasons
非常感谢您这非常好用。。只需将maxseason.startdate更改为maxseason.maxstart