PGError: ERROR: column “p.name” must appear in the GROUP BY clause or be used in an aggregate function

问题:

I get an error with this query. Why? I don't understand :(

    SELECT p.name, p.id, SUM(hours) AS hours, SUM(logged_hours) AS logged_hours     FROM (         SELECT project_id, date, hours, null AS logged_hours         FROM #{ScheduleEntry.table_name}         WHERE user_id = #{User.current.id}             AND date BETWEEN '%s' AND '%s'         UNION         SELECT project_id, spent_on AS date, null AS hours, sum(#{TimeEntry.table_name}.hours) AS logged_hours         FROM #{TimeEntry.table_name}         WHERE user_id = #{User.current.id}             AND spent_on BETWEEN '%s' AND '%s'         GROUP BY project_id, date     ) AS results     LEFT JOIN #{Project.table_name} AS p ON p.id = results.project_id     GROUP BY project_id 

回答1:

Change GROUP BY project_id to GROUP BY p.name,p.id

The docs say:

When GROUP BY is present, it is not valid for the SELECT list expressions to refer to ungrouped columns except within aggregate functions, since there would be more than one possible value to return for an ungrouped column.

文章来源: PGError: ERROR: column “p.name” must appear in the GROUP BY clause or be used in an aggregate function