Sql DISTINCT 从结果中删除列

Question

我有一个简单的 PostgreSQL 查询，它按最近的日期查询事件，但是我想从结果中删除这个不同的列(时间)

SELECT DISTINCT time, sensor_id, event_type, value from events ORDER BY sensor_id

+---------------------+---+---+-----+
| 2014-02-13 12:42:00 | 2 | 2 |   5 |
| 2014-02-13 13:19:57 | 2 | 4 | -42 |
| 2014-02-13 13:32:36 | 2 | 3 |  54 |
| 2014-02-13 14:48:30 | 2 | 2 |   2 |
| 2014-02-13 12:54:39 | 3 | 2 |   7 |
+---------------------+---+---+-----+

需要这样的结果

+---+---+-----+
| 2 | 2 |   5 |
| 2 | 4 | -42 |
| 2 | 2 |   2 |
| 2 | 3 |  54 |
| 3 | 2 |   7 |
+---+---+-----+ 

Answer 1

您可以使用 PostgreSQL DISTINCT ON (...)特点:

SELECT DISTINCT ON (time, sensor_id, event_type, value)
       sensor_id, event_type, value from events
ORDER BY sensor_id;