使用join从sql中的同一张表中获取数据

Question

我有一个表 [dbo].[UserImages]，其中用户每 6 天上传一次照片，用户 3 共有 18 条记录。第 1 天有 9 条记录，第 6 天有 9 条记录。此表中有 4 列 [Id, UserId, Image, Day]

Id  UserId  Image               Day
1   3       3_20200408_1.png    1
2   3       3_20200408_2.png    1
3   3       3_20200408_3.png    1
4   3       3_20200408_4.png    1
5   3       3_20200408_5.png    1
6   3       3_20200408_6.png    1
7   3       3_20200408_7.png    1
8   3       3_20200408_8.png    1
9   3       3_20200408_9.png    1
10  3       3_20200410_9.png    6
11  3       3_20200410_2.png    6
12  3       3_20200410_3.png    6
13  3       3_20200410_4.png    6
14  3       3_20200410_5.png    6
15  3       3_20200410_6.png    6
16  3       3_20200410_7.png    6
17  3       3_20200410_8.png    6
18  3       3_20200410_9.png    6

我需要这样的东西

ImgCount UserId ImageDay1 ImageDay6 1 3 3_20200408_1.png 3_20200408_1.png 2 3 3_20200408_2.png 3_20200408_2.png 3 3 3_20200408_3.png 3_20200408_3.png 4 3 3_20200408_4.png 3_20200408_4.png 5 3 3_20200408_5.png 3_20200408_5.png 6 3 3_20200408_6.png 3_20200408_6.png 7 3 3_20200408_7.png 3_20200408_7.png 8 3 3_20200408_8.png 3_20200408_8.png 9 3 3_20200408_9.png 3_20200408_9.png

我该怎么办

Answer 1

您可以使用row_number() 和聚合：

select
    imgCount,
    userId,
    max(case when day = 1 then image end) ImageDay1,
    max(case when day = 6 then image end) ImageDay6
from (
    select t.*, row_number() over(partition by userId, day order by image) imgCount
    from mytable t
    where day in (1, 6)
) t
group by userId, imgCount
order by ImgCount

Demo on DB Fiddle：

图像计数 |用户名 | ImageDay1 | ImageDay6 :------- | -----: | :--------------- | :--------------- 1 | 3 | 3_20200408_1.png | 3_20200410_1.png 2 | 3 | 3_20200408_2.png | 3_20200410_2.png 3 | 3 | 3_20200408_3.png | 3_20200410_3.png 4 | 3 | 3_20200408_4.png | 3_20200410_4.png 5 | 3 | 3_20200408_5.png | 3_20200410_5.png 6 | 3 | 3_20200408_6.png | 3_20200410_6.png 7 | 3 | 3_20200408_7.png | 3_20200410_7.png 8 | 3 | 3_20200408_8.png | 3_20200410_8.png 9 | 3 | 3_20200408_9.png | 3_20200410_9.png