Question

我有一个带有ID，AID和Year字段的表。如何在集合中找到最近的共同年份（常见的AID组成集合）

ID  AID Year
---------
1   1   2001
2   1   2002
3   1   2003
4   1   2004

5   2   2003
6   2   2004
7   2   2005

8   3   2004
9   3   2005
10  3   2006

最近的普通年份2004

Answer 1

我相信这是最简单的方法。

查询

    SELECT 
      Year
    FROM 
     t
    GROUP BY 
     Year
    HAVING 
     COUNT(*) = (SELECT COUNT(DISTINCT t.AID) FROM t)

结果

    | Year |
    | ---- |
    | 2004 |

请参阅demo

此查询使它更容易理解

查询

SELECT 
     Year
  ,  COUNT(*) AS count_per_AID
  , (SELECT COUNT(DISTINCT t.AID) FROM t) AS unique_count_per_AID
  , (COUNT(*) = (SELECT COUNT(DISTINCT t.AID) FROM t)) AS most_common_value
FROM 
 t
GROUP BY 
 Year

结果

| Year | count_per_AID  | unique_count_per_AID | most_common_value |
| ---- | -------------- | -------------------- | ----------------- |
| 2001 | 1              | 3                    | 0                 |
| 2002 | 1              | 3                    | 0                 |
| 2003 | 2              | 3                    | 0                 |
| 2004 | 3              | 3                    | 1                 |
| 2005 | 2              | 3                    | 0                 |
| 2006 | 1              | 3                    | 0                 |

此查询返回所有普通年份，而不是最新的普通年份年。

确实要感谢您的评论。
解决方法是使用查询

SELECT 
  Year
FROM 
 t
GROUP BY 
 Year
HAVING 
 COUNT(*) = (SELECT COUNT(DISTINCT t.AID) FROM t)
ORDER BY 
 t.Year DESC
LIMIT 1
;

请参阅demo

如何使用MySQL查询从集合中获得共同价值？

1 个答案: