我想将多行合并为一，只保留值不为NULL的值
这是我要实现的目标：
我要这个
+----+-----------------+-----------------+-----------------+--------------------+
| ID | 1stNofification | 2ndNotification | 3rdNotification | NotificationNumber |
+----+-----------------+-----------------+-----------------+--------------------+
| 1 | 01.01.2019 | NULL | NULL | 1 |
+----+-----------------+-----------------+-----------------+--------------------+
| 1 | NULL | 02.02.2019 | NULL | 2 |
+----+-----------------+-----------------+-----------------+--------------------+
| 1 | NULL | NULL | 03.03.2019 | 3 |
+----+-----------------+-----------------+-----------------+--------------------+
| 2 | 06.01.2019 | NULL | NULL | 1 |
+----+-----------------+-----------------+-----------------+--------------------+
| 2 | NULL | 09.02.2019 | NULL | 2 |
+----+-----------------+-----------------+-----------------+--------------------+
| 2 | NULL | NULL | 11.03.2019 | 3 |
+----+-----------------+-----------------+-----------------+--------------------+
对此：
+----+-----------------+-----------------+-----------------+
| ID | 1stNofification | 2ndNotification | 3rdNotification |
+----+-----------------+-----------------+-----------------+
| 1 | 01.01.2019 | 02.02.2019 | 03.03.2019 |
+----+-----------------+-----------------+-----------------+
| 2 | 06.01.2019 | 09.02.2019 | 11.03.2019 |
+----+-----------------+-----------------+-----------------+
我尝试过类似的事情：
SELECT
ID,
MAX(CASE WHEN a.NotificationNumber = 1 THEN 1stNotification END)1stNotification,
MAX(CASE WHEN a.NotificationNumber = 2 THEN 2ndNotification END)2ndNotification,
MAX(CASE WHEN a.NotificationNumber = 3 THEN 3rdNotification END)3rdNotification
FROM Notifications
GROUP BY ID
不幸的是，那并没有给我我预期的结果。
如果有人可以帮助我，我将非常感激：）
答案 0 :(得分：4)
您只需要在没有任何情况下使用max
SELECT
ID,
MAX(1stNotification) AS 1stNotification,
MAX(2ndNotification) AS 2ndNotification,
MAX(3rdNotification) AS 3rdNotification
FROM Notifications
GROUP BY ID
答案 1 :(得分：0)
我认为您需要这样的东西...
isinstance据我所知，这里的通知列实际上是行中提到的通知编号。