我想在 postgres SQL 中按日期和时间对我的数据进行分组，并希望每个 groupby 列中有一行

Question

I want to fetch data from history table and I want to group by usergroupid and I want only one row of usergroupid 237935 and 761793 out of multiple rows.

I get this error

Column "history.entrytime" must appear in the GROUP BY clause or be used in an aggregate function

This is my query:

SELECT  
    TO_CHAR(entrytime, 'YYYY-MM-DD HH12:MI'), usergroupid 
FROM 
    "public"."history" 
WHERE 
    deviceid = 17355763  usergroupid IN (237935,761793) 
GROUP BY 
    TO_CHAR(entrytime, 'YYYY-MM-DD HH12:MI'), usergroupid 
ORDER BY
    entrytime DESC 
LIMIT 1

I want following output:

to_char	usergroupid
2022-11-19 02:04:10	237935
2022-11-19 02:05:40	761793

This is my demo table:

Answer 1

It seems you simply want the maximum entrytime per usergroupid. In order to get one row per usergroupid, you GROUP BY usergroupid . In order to get the maximum entrytime, you select MAX(entrytime) .

SELECT  MAX(entrytime), usergroupid
FROM public.history
WHERE deviceid = 17355763 AND usergroupid IN (237935,761793) 
GROUP BY usergroupid
ORDER BY usergroupid;