对同一张表中的用户数求和并计数

Question

给定以下表格结构，我想将仅上传 1 个文件、2 个文件、3 个文件一直到 n 个文件的用户数相加。

我正在努力解决这个查询 - 任何指针？

TABLE

+----+--------+-----------+---------------------+
| Id | UserId | FileName  | CreatedAt           |
+----+--------+-----------+---------------------+
| 1  | 4      | test.jpg  | 2019-09-05 14:42:12 |
| 2  | 4      | truth.png | 2019-09-05 14:42:12 |
| 3  | 5      | gen.jpg   | 2019-09-05 14:42:12 |
| 4  | 6      | bob.jpg   | 2019-09-05 14:42:12 |
+----+--------+-----------+---------------------+

DESIRED OUTCOME

+-----------------+------------------+
| Number of Items | Count            |
+-----------------+------------------+
| 1 uploaded      | 2 users          |
| 2 uploaded      | 1 users          |
+-----------------+------------------+

Answer 1

首先，使用GROUP BY和COUNT(*)聚合，在子查询中获取特定用户上传的文件数。 之后，您可以将此结果集用作派生表，以计算具有相同上传次数的用户数（按先前计算的计数分组）：

SELECT 
  dt.total_files_uploaded, 
  COUNT(dt.UserId) AS num_of_users
FROM 
( 
  SELECT UserId, COUNT(*) AS total_files_uploaded
  FROM your_table 
  GROUP BY UserId
) AS dt
GROUP BY dt.total_Files_uploaded

Answer 2

SELECT ab.UploadedFiles, COUNT(ab.UserId) AS NumUsers
( SELECT UserId, COUNT(*) AS UploadedFiles 
  FROM table_name 
  GROUP BY UserId
) AS ab

干杯