根据行中的标记获取变量最小日期

Question

我正在使用 MySQL 和 phpMyAdmin，下面是我的数据 table:

+--------+---------+-----------------+
| userID | context |      time       |
+--------+---------+-----------------+
|    111 |         | 7/1/2021        |
|    111 |         | 7/16/2019       |
|    111 | Reset   | 7/15/2019       |
|    222 |         | 7/9/2020        |
|    222 | Reset   | 7/8/2020        |
|    333 | Reset   | 5/11/2020       |
|    333 |         | 5/10/2020       |
|    444 |         | 9/8/2020        |
+--------+---------+-----------------+

我正在寻找一个 SELECT 查询，它给我 MIN 时间大于或等于 Reset 在context 列。如果 Reset 标记不存在于 context 列中，我希望包含结果。

所以对于上面的table，我期望结果：

+--------+-----------------+
| userID |      time       |
+--------+-----------------+
|    111 | 7/15/2019       |
|    222 | 7/8/2020        |
|    333 | 5/11/2020       |
|    444 | 9/8/2020        |
+--------+-----------------+

我试过了：

SELECT * FROM foo as a 
WHERE ((SELECT MIN(a.time) FROM foo) >= (SELECT Max(a.time) FROM foo where context = 'Reset')) group by userID

没有产生我预期的输出，但是 returns:

+--------+-----------+
| userID |   time    |
+--------+-----------+
|    111 | 7/1/2021  |  <--- wrong 
|    222 | 7/8/2020  |
|    333 | 5/11/2020 |
+--------+-----------+

Answer 1

根据您的预期结果，您可以尝试以下查询 -

SELECT userID, MAX(time)
  FROM YOUR_TABLE
 WHERE context = 'RESET'
 GROUP BY userID
 UNION ALL
SELECT userID, MAX(time)
  FROM YOUR_TABLE
 WHERE context IS NULL
 GROUP BY userID
 ORDER BY userID

Answer 2

使用window函数：

select t.*,
       coalesce(next_time, time) as imputed_time
from (select t.*,
             sum(context = 'reset') over (partition by user_id) as cnt_reset,
             min(case when context is null then time end) over (partition by userid order by time rows between current row and unbounded following) as next_time
      from t
     ) t
where cnt_reset = 0 or context = 'reset';

根据行中的标记获取变量最小日期

Get variable MIN Date based on marker in row

mysql

sql

subquery