在 Rails 3.1 上使用子查询作为表答案

【问题标题】：using subquery as a table on rails 3.1在 Rails 3.1 上使用子查询作为表
【发布时间】：2012-02-21 19:18:45
【问题描述】：

我正在尝试从另一个查询中选择一些数据。 SQL 将如下所示：

SELECT user_id, rank FROM 
(SELECT user_id, MAX(created_at) as latest_solution, COUNT(*) AS solved,
rank() OVER (ORDER by COUNT(*) desc) AS rank FROM submissions group by user_id) 
as leaderboard WHERE leaderboard.user_id = xx

但我在尝试将其翻译成 activerecord 语言时遇到了麻烦

我认为我可以使用以下子查询：

Submission.select('user_id, MAX(created_at) as latest_solution, COUNT(*) as solved, rank() OVER (ORDER BY count(*) desc) as rank').group('user_id')

但我不知道如何将其用作“表格”。

【问题讨论】：

标签： sql ruby-on-rails ruby-on-rails-3 activerecord subquery

【解决方案1】：

我直接去find_by_sql 询问任何重要的事情：

Submission.find_by_sql(%q{
    select user_id,
           rank
    from (
        select user_id,
               max(created_at) as latest_solution,
               count(*) AS solved,
               rank() over (order by count(*) desc) as rank
        from submissions
        group by user_id
    ) as leaderboard
    where leaderboard.user_id = :user_id
}, :user_id => 'xx')

将其包装在Submission 上的类方法中，您应该没问题。

【讨论】：