给出以下形式的postgres表:
group id | timestamp | value
---------+-------------------------------+------
1 | 2020-04-15 15:04:44.020288+00 | 8.0
2 | 2020-04-15 15:05:44.020288+00 | 9.0
3 | 2020-04-15 15:06:44.020288+00 | 10.0
4 | 2020-04-15 15:07:44.020288+00 | 11.0
1 | 2020-04-15 15:08:44.020288+00 | 12.0
2 | 2020-04-15 15:09:44.020288+00 | 13.0
3 | 2020-04-15 15:10:44.020288+00 | 14.0
4 | 2020-04-15 15:11:44.020288+00 | 15.0
根据时间戳列检索组ID子集的最后一行的SQL查询是什么?
例如,检索组ID {1,3}
的最后一行以产生:
group id | timestamp | value
---------+-------------------------------+------
1 | 2020-04-15 15:08:44.020288+00 | 12.0
3 | 2020-04-15 15:10:44.020288+00 | 14.0
提前感谢您的考虑和回复
解决Postgres中的每组最大n个问题的简单有效的方法是使用distinct on
:
select distinct on (group_id) t.*
from mytable t
where group_id in (1, 3)
order by group_id, timestamp desc