内部联接

Question

我正在努力使用Rails的ActiveRecord查询接口来复制具有内部联接子查询的查询。我将如何复制以下内容：

SELECT ass.name, COUNT(DISTINCT a.question_id) AS 
  answered_questions, tq.total_questions
  FROM assessments AS ass
  INNER JOIN  (SELECT ass.id, COUNT(q.id) AS total_questions FROM                         
    questions AS q INNER JOIN assessments AS ass ON ass.id=q.assessment_id 
    GROUP BY 
    ass.id) as tq ON tq.id=ass.id
  INNER JOIN questions AS q ON q.assessment_id=ass.id
  INNER JOIN answers AS a ON a.assessment_id=ass.id AND a.question_id=q.id
  INNER JOIN org_assesments AS oa ON ass.id=oa.assessment_id
  INNER JOIN users AS u ON oa.org_id=u.org_id AND       
    a.user_id=u.id
  WHERE  u.id=1
  GROUP BY ass.name, tq.total_questions
  ORDER BY ass.created_at DESC
  LIMIT 10

我似乎无法使用查询构建器使用子查询。如果没有子查询，我就会这样做，并且会给出评估标题和回答的问题数量：

Question.joins(:assessment => {:org_assessments => {:org => :users}}).joins(:answers)
                 .where(answers:{:user_id => params[:id]})
                 .distinct('answers.question_id').group(['assessments.name']).count()

如何编写此代码以包含上述原始SQL中的子查询？

Answer 1

您可以将子查询作为字符串发送到joins方法：

subquery =
  TotalQuestion.
    join(:assessments).
    group('assessments.id').
    select('assessments.id, COUNT(q.id) as total_questions').to_sql

Question.joins("(#{sub_query}) as tq on tq.id=ass.id")

您可以将其与查询的其他部分结合使用：

Question.
    joins(:assessment => {:org_assessments => {:org => :users}}).joins(:answers).
    joins("(#{sub_query}) as tq on tq.id=ass.id").
    where(answers:{:user_id => params[:id]}).
    distinct('answers.question_id').group(['assessments.name']).count()