Question

我有一个名为 transactions 的表，其中包含所有事务。像这样：

// transactions
+--------+-------------+---------+-------------+---------------------+
|  id    | business_id | user_id |   amount    |      created_at     |
+--------+-------------+---------+-------------+---------------------+
| 1      | 503         | 12      | 4500        | 2021-04-15 04:22:09 |
| 2      | 33          | 12      | 1200        | 2021-04-17 12:22:10 |
| 3      | 771         | 13      | 400         | 2021-04-18 13:02:18 |
| 4      | 86          | 14      | 7500        | 2021-04-18 16:07:12 | 
| 5      | 772         | 13      | 3400        | 2021-04-23 07:11:04 |
| 6      | 652         | 14      | 900         | 2021-04-24 10:35:08 |
| 7      | 567         | 15      | 1000        | 2021-04-24 14:55:11 |
+--------+-------------+---------+-------------+---------------------+

我需要计算每天第一笔交易的用户数量。所以这是预期的结果：

// The expected result
+------+-------+-------+--------------------------+
| year | month |  day  |  first_transactions_num  |
+------+-------+-------+--------------------------+
| 2021 | 04    | 15    | 1                        |
| 2021 | 04    | 18    | 2                        |
| 2021 | 04    | 24    | 1                        |
+------+-------+-------+--------------------------+

知道我该怎么做吗？

这是我尝试过的：

SELECT year(created_at) year,
       month(created_at) month,
       day(created_at) day,
       count(1) num
FROM transactions
GROUP BY year, month, day

但是我的查询并不关心“每个用户的第一笔交易”。

Answer 1

您应该汇总此查询的结果：

SELECT MIN(created_at) created_at
FROM transactions
GROUP BY user_id

返回每个用户的第一笔交易。
所以这样做：

SELECT YEAR(created_at) year,
       MONTH(created_at) month,
       DAY(created_at) day,
       COUNT(*) num
FROM (
  SELECT MIN(created_at) created_at
  FROM transactions
  GROUP BY user_id
) t
GROUP BY year, month, day

或者更好：

SELECT YEAR(created_at) year,
       MONTH(created_at) month,
       DAY(created_at) day,
       COUNT(*) num
FROM (
  SELECT DATE(MIN(created_at)) created_at
  FROM transactions
  GROUP BY user_id
) t
GROUP BY created_at

或者如果您的 MySql 版本是 8.0+，请使用 COUNT() 窗口函数：

SELECT DISTINCT 
       YEAR(MIN(created_at)) year,
       MONTH(MIN(created_at)) month,
       DAY(MIN(created_at)) day,
       COUNT(*) OVER (PARTITION BY DATE(MIN(created_at))) num
FROM transactions
GROUP BY user_id

参见demo。

如何统计每个用户每天的第一笔交易次数？

1 个答案: