想要删除 SQL 中的重复项

Question

我正在用 rails 创建一个应用程序。
我不知道如何编写 SQL 语句，所以请教我。

想要

由此，通过“competition_id”缩小范围并仅提取具有最小“id”的项目。

例如，

+----------------+----+---------------------------+----------------+-------+-----+
| competition_id | id | image                     | name           | count | rnk |
+----------------+----+---------------------------+----------------+-------+-----+
|              1 |  4 | monster4.jpeg             | monster4       |     7 |   1 |
|              2 |  6 | monster2.jpeg             | monster2       |     1 |   1 |
|              3 |  9 | monster1.jpeg             | monster1       |     1 |   1 |
|              5 | 22 | drink_sample.jpeg         | drink6         |     2 |   1 |
|              6 | 33 | sumo_wrestler_sample.jpeg | sumo_wrestler7 |     2 |   1 |
|              7 | 40 | movie_sample.jpeg         | movie4         |     2 |   1 |
|              8 | 50 | food_sample.jpeg          | food4          |     2 |   1 |
|              9 | 61 | color_sample.jpeg         | color5         |     3 |   1 |
|             10 | 72 | book_sample.jpeg          | book6          |     2 |   1 |
|             11 | 82 | book_sample.jpeg          | book6          |     3 |   1 |
+----------------+----+---------------------------+----------------+-------+-----+

当前状态

+----------------+----+---------------------------+----------------+-------+-----+
| competition_id | id | image                     | name           | count | rnk |
+----------------+----+---------------------------+----------------+-------+-----+
|              1 |  4 | monster4.jpeg             | monster4       |     7 |   1 |
|              2 |  6 | monster2.jpeg             | monster2       |     1 |   1 |
|              3 |  9 | monster1.jpeg             | monster1       |     1 |   1 |
|              5 | 22 | drink_sample.jpeg         | drink6         |     2 |   1 |
|              6 | 33 | sumo_wrestler_sample.jpeg | sumo_wrestler7 |     2 |   1 |
|              6 | 34 | sumo_wrestler_sample.jpeg | sumo_wrestler8 |     2 |   1 |
|              6 | 35 | sumo_wrestler_sample.jpeg | sumo_wrestler9 |     2 |   1 |
|              7 | 40 | movie_sample.jpeg         | movie4         |     2 |   1 |
|              7 | 43 | movie_sample.jpeg         | movie7         |     2 |   1 |
|              7 | 45 | movie_sample.jpeg         | movie9         |     2 |   1 |
|              8 | 50 | food_sample.jpeg          | food4          |     2 |   1 |
|              8 | 56 | food_sample.jpeg          | food10         |     2 |   1 |
|              9 | 61 | color_sample.jpeg         | color5         |     3 |   1 |
|             10 | 72 | book_sample.jpeg          | book6          |     2 |   1 |
|             11 | 82 | book_sample.jpeg          | book6          |     3 |   1 |
+----------------+----+---------------------------+----------------+-------+-----+

提取这个的代码

SELECT * FROM (SELECT *,RANK() OVER (PARTITION BY competition_id ORDER BY COUNT DESC) rnk FROM (SELECT items.competition_id,items.id,items.image,items.name,count(*) AS count FROM chosenitems INNER JOIN items ON chosenitems.item_id = items.id GROUP BY items.competition_id,items.id) AS t) AS tt WHERE rnk = 1;

表结构

• 选定项表

ID	session_id	item_id
1	1	2
2	1	3
2	1	2
2	1	2
2	1	5
3	1	7
4	1	4
5	1	5

• 项目表

ID	姓名	图片	比赛编号
1	一个	图像1	1
2	b	图2	1
2	c	图2	1
2	d	图2	1
2	e	图5	2
3	F	图 9	2
4	G	图4	2
5	H	图5	2

我试过了

SELECT * FROM (SELECT *,RANK() OVER (PARTITION BY competition_id ORDER BY COUNT DESC) rnk FROM (SELECT items.competition_id,items.id,items.image,items.name,count(*) AS count FROM chosenitems INNER JOIN items ON chosenitems.item_id = items.id GROUP BY items.competition_id,items.id) AS t) AS tt WHERE id in (SELECT MIN(id) FROM chosenitems GROUP BY competition_id);

↓

失败

+----------------+----+---------------+----------+-------+-----+
| competition_id | id | image         | name     | count | rnk |
+----------------+----+---------------+----------+-------+-----+
|              1 |  1 | monster1.jpeg | monster1 |     4 |   2 |
+----------------+----+---------------+----------+-------+-----+

我想从“rnk”为1的每个“competition_id”中提取ID最小的那个。

环境

macOS 大苏尔
ruby 2.7.0
导轨 6.1.1
mysql 版本 8.0.23

Answer 1

这应该会给您想要的结果，您必须检查MIN是否是每个值的正确选择

SELECT 
    competition_id
    ,MIN(id) as id
    ,MIN(mage) as image
    ,MIN(ame) as name
    ,MIN(count) as count
   ,MIN(rnk) as rnk
FROM 
    (SELECT 
        *
        ,RANK() OVER (PARTITION BY competition_id ORDER BY COUNT DESC) rnk 
    FROM (SELECT 
            items.competition_id
            ,items.id
            ,items.image
            ,items.name
            ,count(*) AS count 
        FROM 
            chosenitems INNER JOIN items ON chosenitems.item_id = items.id 
            GROUP BY items.competition_id,items.id) AS t) AS tt 
WHERE rnk = 1
GROUP BY competition_id;