Question

我有一张有汽车记录的桌子：

table: cars

columns:
car_id | timestamp | km_driven

我正在运行PostgreSQL 9.6。

我该怎么做：

SELECT timestamp, car_id, km_driven_within_the_hour FROM cars

我想GROUP BY我的timestamp，以便将每小时记录的所有记录按每辆车分组，然后在该小时内将km_driven_within_the_hour SUM合并在一起。

我尝试过：

SELECT timestamp, car_id, SUM(km_driven) AS km_driven_within_the_hour
FROM cars
GROUP BY trunc(EXTRACT(hour from timestamp)), car_id

给我错误：

ERROR:  function pg_catalog.date_part(unknown, text) does not exist

以及投放时间戳记：

SELECT timestamp, car_id, SUM(km_driven) AS km_driven_within_the_hour
FROM cars
GROUP BY trunc(EXTRACT(hour from timestamp::timestamp)), car_id

给我：

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

Answer 1

您快到了。按小时替换timestamp，如下所示：

SELECT
    trunc(EXTRACT(hour from timestamp::timestamp)), 
    car_id, 
    SUM(km_driven) AS km_driven_within_the_hour
  FROM cars
  GROUP BY trunc(EXTRACT(hour from timestamp::timestamp)), car_id

PostgreSQL-GROUP BY时间戳和car_id

1 个答案: