PostgreSQL，GROUP BY和Window函数

Question

我在PostgreSQL中得到以下查询，该查询可以显示记录：

'SELECT TO_CHAR(date_trunc(\'hour\', time::timestamp), \'YYYY-MM-DD HH24:MI:SS\') AS time_from,
        TO_CHAR(date_trunc(\'hour\', time::timestamp) + interval \'1 hour\', \'YYYY-MM-DD HH24:MI:SS\') AS time_to,
        SUM(km) AS km
 FROM cars 
 GROUP BY date_trunc(\'hour\', time::timestamp) LIMIT 1000 OFFSET 50'

我想添加SUM(km) OVER() as km_total来获得km的总数，因为查询中有limit和offset。

但是然后我得到了错误：

error: column "cars.km" must appear in the GROUP BY clause or be used in an aggregate function

但是我不允许将其添加到我的GROUP BY中，这给了我以下错误：

error: window functions are not allowed in GROUP BY

Answer 1

您要

   SUM(SUM(km)) OVER () AS total_km

一开始SUM()的嵌套看起来很奇怪。内部SUM(km)是聚合函数。外部SUM()是窗口函数。