mysql - 根据MySQL中的两列查找最小值

Question

我在 MySQL 中有一个包含运动表现的表。

结构:

id (PRIMARY KEY)    
athlete_id (FOREIGN KEY)    
perform     
category_id     
discipline_id

如果我想从此表中选择最佳表现(每个运动员最多只能进入一次结果)，我使用以下查询:

SELECT 
  * 
FROM
  performs NATURAL 
  JOIN athletes 
  JOIN 
    (SELECT 
      athlete_id,
      MIN(perform) AS perform,
      category_id,
      discipline_id 
    FROM
      zaznamy 
    WHERE discipline_id = 4 
      AND category_id = 3 
    GROUP BY athlete_id) rec 
    ON performs.athlete_id = rec.athlete_id 
    AND performs.perform = rec.perform 
    AND performs.category_id = rec.category_id 
    AND performs.discipline_id = rec.discipline_id 
ORDER BY performs.perform 
LIMIT 25 

我得到了正确的结果。但我想从一个学科和多个类别中选出最好的表现(例如男子与青少年等)。如何对两列使用子句 GROUP BY？

Answer 1

也许我不明白什么，但是您可以在分组依据中添加两列，如下例所示。只需在两列或多列之间添加 ,(逗号)即可。

SELECT 
* 
FROM
  performs NATURAL 
  JOIN athletes 
  JOIN 
    (SELECT 
      athlete_id,
      MIN(perform) AS perform,
      category_id,
      discipline_id 
    FROM
      zaznamy 
    WHERE discipline_id = 4 
    GROUP BY athlete_id,category_id) rec 
    ON performs.athlete_id = rec.athlete_id 
    AND performs.perform = rec.perform 
    AND performs.category_id = rec.category_id 
    AND performs.discipline_id = rec.discipline_id 
ORDER BY performs.perform 
LIMIT 25 enter code here

编辑 - 更新

好的，现在我明白你的问题了。实际上，这很常见，您希望首先找到组的最大值，然后请求有关该值的附加信息。

实现此目的的一种方法是使用如下的嵌套查询

SELECT ss.athlete_id,ss.perform,category_id
FROM performs ss
inner join
(SELECT
    athlete_id, MIN(perform) AS perform
FROM 
    performs
WHERE
    discipline_id = 4 AND category_id IN (1,3,5,7,9) 
GROUP BY
    athlete_id) tt
    on tt.athlete_id = ss.athlete_id and ss.perform = tt.perform

结果就是您上面描述的结果。