PGError：错误：列“p.name”必须出现在 GROUP BY 子句中或在聚合函数中使用

Question

我收到此查询错误。为什么？我不明白 ：（

    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

Answer 1

将 GROUP BY project_id 更改为 GROUP BY p.name,p.id

文档 说：

当存在 GROUP BY 时，SELECT 列表表达式引用未分组的列（聚合函数内除外）是无效的，因为可能有多个可能为未分组的列返回的值。