MySQL SELECT 从多个表，多个 GROUP BY 和 group_concat？

Posted 2023-02-24

【中文标题】MySQL SELECT 从多个表，多个 GROUP BY 和 group_concat？

【英文标题】：MySQL SELECT from multiple tables, multiple GROUP BY and group_concat?

【发布时间】：2012-07-10 01:05:56

【问题描述】：

我想在 MySQ 中查询三个表。如下：

**Table: Leaderboard**
Name  | Score
------------
James | 1
Steve | 2
Dave  | 5

**Table: Actions**
Name  | Action       | Time
----------------------------
James | Ate an apple | 01:00
James | Kicked a dog | 02:00
Steve | Ate a dog    | 03:00
Steve | Kicked a hen | 01:00
Dave  | died         | 02:00

**Table: Items**
Name  | Item         | Time
----------------------------
James | Chainsaw     | 01:00
James | Hammer       | 01:05
James | Crowbar      | 01:10
Steve | Hammer       | 02:00
Steve | Egg          | 01:05
Dave  | Egg          | 01:05

我需要一个查询来选择每个玩家（ORDER BY Leaderboard.score DESC）并选择他们最新的 Action WHERE Actions.action LIKE 'Ate %'，然后给出所有 Items.Item ORDER BY Time DESC

例如，输出将如下所示

**Output**
Name   | Latest_Action | Items
Steve  | Ate a dog     | Hammer, Egg
James  | Ate an apple  | Crowbar, Hammer, Chainsaw

到目前为止，我已经尝试了以下查询，但它在 group_concat 中多次返回每个项目

SELECT Leaderboard.Name, Actions.*, group_concat(Items.Item)
FROM Leaderboard, Actions, Items
WHERE Items.Name = Actions.Name
  AND Actions.Action LIKE 'Ate %'
  AND Actions.Name IN (SELECT Name FROM Leaderboard ORDER BY SCORE DESC)
GROUP BY Leaderboard.name

非常感谢任何帮助！

【问题讨论】：

您无法使用子查询对结果进行排序：外部 GROUP BY 将覆盖目前存在的任何排序。

【参考方案1】：

SELECT Leaderboard.Name,
  (SELECT Actions.Action
   FROM Actions
   WHERE Actions.Name = Leaderboard.Name
     AND Actions.Action LIKE 'Ate%'
   ORDER BY Time DESC
   LIMIT 1
  ) AS Latest_Action,
  GROUP_CONCAT(Items.Item
               ORDER BY Items.Time DESC
               SEPARATOR ', '
              ) AS Items
FROM Leaderboard
     LEFT JOIN Items ON Leaderboard.Name = Items.Name
GROUP BY Leaderboard.Name
HAVING Latest_Action IS NOT NULL
ORDER BY Leaderboard.Score DESC

结果在SQL Fiddle 中验证。

【讨论】：

制作：GROUP_CONCAT(Items.Item SEPARATOR ', ' ORDER BY Items.Time DESC)

@ypercube：谢谢，错过了那部分。

这完全按照要求工作，非常感谢。如何从 Actions 表中选择多个列？

@user1491032：讨论这个问题将超出此类评论的范围，特别是在源代码格式化功能方面。最好问一个关于这个的后续问题。