列必须出现在 GROUP BY 子句中或在聚合函数中使用 [重复]

Question

所以我在 postgreSQL（以及其他）中有提交、用户、故事和视图表，如下所示：

submissions
-----------
user_id
story_id
body

views
-----------
user_id
submissions_id

users
-----------
username

我有一个复杂的 SQL 查询查找，它返回的提交按用户是否看过它排序（在 views 表中有一个 user_id 和 submit_id 条目），然后按它有多少视图：

    submissions.find_by_sql("select submissions.*,
          count(views.submission_id) as views_count,
          (select count(*) from views
            where views.user_id=#{user_id} and views.submission_id=submissions.id group by id) as counted
          from submissions
          left outer join views on views.submission_id=submissions.id
          where submissions.story_id = #{id}
          group by submissions.id
          order by counted desc, views_count")

我还希望能够获取每次提交的用户名，这应该很容易：只需在 users.id=submissions.user_id 处加入用户表并将 users.username 添加到选择部分。但是，当我这样做时，我收到一个错误

column "users.username" must appear in the GROUP BY clause or be used in an aggregate function 

这不应该，因为将用户添加到 group by 会删除具有相同用户的多个提交，并且我不需要聚合函数。

由于我显然必须明确说明这一点，我知道还有很多其他问题在问这个问题，但没有一个真正回答我的问题。

Answer 1

当你有一个group by 子句时，在大多数系统中你被限制在 仅在您的 select 语句中显示 group by 子句中的字段。加上使用 count(), sum(), 等的任何聚合列

尝试围绕您的原始查询进行另一个查询：

select * from 
(
select top 100 percent 
          submissions.id,
          count(views.submission_id) as views_count,
          (select count(*) from views
            where views.user_id=#{user_id} and views.submission_id=submissions.id group by id) as counted
          from submissions
          left outer join views on views.submission_id=submissions.id
          where submissions.story_id = #{id}
          group by submissions.id
          order by counted desc, views_count
) as InnerQuery
left join submissions on submissions.ID = InnerQuery.ID