MySQL子查询没有给我MAX或ORDER BY LIMIT 1的最高值答案

【问题标题】：MySQL subquery does not give me the highest value with MAX or ORDER BY LIMIT 1MySQL子查询没有给我MAX或ORDER BY LIMIT 1的最高值
【发布时间】：2017-08-02 00:39:54
【问题描述】：

我的 MySQL 查询有问题。它的子查询没有给出last.id 的最大值。

SELECT rounds.winners, rounds.losers
FROM players
INNER JOIN teams ON teams.id = players.ilmo_id
INNER JOIN status AS first ON first.id = players.status_id
LEFT JOIN matches ON matches.chart_id = 12
  AND matches.id = (
    SELECT  last.id
    FROM    matches AS last
    WHERE   (last.player1_id = players.id
            OR last.player2_id = players.id
            OR last.player3_id = players.id
            OR last.player4_id = players.id)
            ORDER BY last.id DESC
            LIMIT 1
        )

 JOIN charts ON charts.id = matches.chart_id
 JOIN places ON charts.template_id = places.template_id AND places.id = matches.place_id
 JOIN templates ON places.template_id = templates.id
 JOIN rounds ON places.round_id = rounds.id
 WHERE players.comp_id = 12

这个方法我也试过了，但是不行：

SELECT rounds.winners, rounds.losers
FROM players
INNER JOIN teams ON teams.id = players.ilmo_id
INNER JOIN status AS first ON first.id = players.status_id
LEFT JOIN matches ON matches.chart_id = 12
  AND matches.id = (
    SELECT  MAX(last.id)
    FROM    matches AS last
    WHERE   (last.player1_id = players.id
            OR last.player2_id = players.id
            OR last.player3_id = players.id
            OR last.player4_id = players.id)
        )

 JOIN charts ON charts.id = matches.chart_id
 JOIN places ON charts.template_id = places.template_id AND places.id = matches.place_id
 JOIN templates ON places.template_id = templates.id
 JOIN rounds ON places.round_id = rounds.id
 WHERE players.comp_id = 12

编辑：

这是最新版本，似乎可以正常工作。

SELECT rounds.winners, rounds.losers
FROM players
INNER JOIN teams ON teams.id = players.ilmo_id
INNER JOIN status AS first ON first.id = players.status_id
LEFT JOIN matches ON matches.chart_id = 12
  AND matches.id = (
    SELECT  last.id
    FROM    matches AS last
    WHERE   last.chart_id = 12 /* modified */
            AND (last.player1_id = players.id
            OR last.player2_id = players.id
            OR last.player3_id = players.id
            OR last.player4_id = players.id)
            ORDER BY last.place_id DESC /* modified */
            LIMIT 1
        )

 JOIN charts ON charts.id = matches.chart_id
 JOIN places ON charts.template_id = places.template_id AND places.id = matches.place_id
 JOIN templates ON places.template_id = templates.id
 JOIN rounds ON places.round_id = rounds.id
 WHERE players.comp_id = 12

【问题讨论】：

之前几乎可以肯定地问过和回答过数千次，但如果仍然挣扎，请参阅meta.stackoverflow.com/questions/333952/…
你要参加什么比赛？ on 子句看起来更像是 where 子句的条件。您正在加入匹配，其中chart_id = 12 并且它是最高ID，但在您的子查询中，您没有引用chart_id。它返回所有chart_ids 的最高ID。所以如果最高ID行没有chart_id = 12，on子句将不匹配。
@LAS 现在我的子查询有 WHERE last.chart_id = 12 AND (last.player1_id... 好吗？
是的，我现在明白了。我认为您不需要在 ON 之后立即使用 matches.chart_id = 12。这是多余的，因为它在子查询中处理。

标签： mysql sql database subquery

【解决方案1】：

SELECT rounds.winners, rounds.losers
FROM players
INNER JOIN teams ON teams.id = players.ilmo_id
INNER JOIN status AS first ON first.id = players.status_id
LEFT JOIN matches ON matches.id = (
    SELECT  max(last.id)
    FROM    matches AS last
    WHERE   last.chart_id = 12 /* modified */
            AND (last.player1_id = players.id
            OR last.player2_id = players.id
            OR last.player3_id = players.id
            OR last.player4_id = players.id)
        )
 JOIN charts ON charts.id = matches.chart_id
 JOIN places ON charts.template_id = places.template_id AND places.id = matches.place_id
 JOIN templates ON places.template_id = templates.id
 JOIN rounds ON places.round_id = rounds.id
 WHERE players.comp_id = 12

【讨论】：

你认为max(last.id) 比使用order by 和limit 1 更好吗？
只是因为它是跨平台的标准。但我会使用性能最佳的语法。