每时每刻获取某列中所有过去值都为空的行

Question

假设我有一个带有 ID、时间戳和另一列的 MySQL 表。我的应用程序每 15 分钟为每个 ID 添加一行，列中包含 null 或其他值。最终，新的 ID 可能会出现或消失。

+----+------+--------+
| ID | time | column |
+----+------+--------+
| 1  | 8:00 | A      |
+----+------+--------+
| 2  | 8:00 | null   |
+----+------+--------+
| 3  | 8:00 | B      |
+----+------+--------+
| 4  | 8:00 | null   |
+----+------+--------+
| 1  | 8:15 | A      |
+----+------+--------+
| 2  | 8:15 | null   |
+----+------+--------+
| 3  | 8:15 | null   |
+----+------+--------+
| 4  | 8:15 | null   |
+----+------+--------+
| 5  | 8:15 | null   |
+----+------+--------+
| 1  | 8:30 | A      |
+----+------+--------+
| 2  | 8:30 | null   |
+----+------+--------+
| 3  | 8:30 | B      |
+----+------+--------+
| 4  | 8:30 | C      |
+----+------+--------+
| 5  | 8:30 | null   |
+----+------+--------+
| 1  | 8:45 | A      |
+----+------+--------+
| 2  | 8:45 | null   |
+----+------+--------+
| 3  | 8:45 | null   |
+----+------+--------+
| 4  | 8:45 | C      |
+----+------+--------+
| 5  | 8:45 | D      |
+----+------+--------+

我想要一个查询，为每个时间戳提供当前行和过去行中列中为空的所有行。

预期结果：

+----+------+
| ID | time |
+----+------+
| 2  | 8:00 |
+----+------+
| 4  | 8:00 |
+----+------+
| 2  | 8:15 |
+----+------+
| 4  | 8:15 |
+----+------+
| 5  | 8:15 |
+----+------+
| 2  | 8:30 |
+----+------+
| 5  | 8:30 |
+----+------+
| 2  | 8:45 |
+----+------+

谢谢。

Answer 1

我认为以下查询应该适合您。它正在检查每个 id 是否在当前行和上一行的 'col' 中有 null。

SELECT 
    t1.id, t1.time
FROM
    test t1
WHERE
    t1.col IS NULL
    AND ((SELECT MAX(col) FROM test WHERE id = t1.id AND time < t1.time) IS NULL);