利用find来引导SQL查询 [英] Rails SQL Query with find

问题描述

  select id，name from questions 
 where id not in（从level_questions where level_id = 15中选择question_id）
  

我该怎么做？我正在使用Rails框架和MySQL。
在此先感谢。

解决方案

简单的方法：

<$ collect（&：question_id）$ b（pre：<= c $ c> ids = LevelsQuestion.all（：select =>question_id，
：conditions =>level_id = 15 $ b Question.all（：select =>id，name，：conditions => [id not in（？），ids]）

  Question.all（：select => id，name，
：conditions => [id not in（from level_questions where level_id = 15 select question_id）]）
  

I want this SQL query to be written in rails controller using find:

select id,name from questions
where id not in (select question_id from levels_questions where level_id=15)

How will I do this? I am using Rails framework and MySQL. Thanks in advance.

解决方案

Simple way:

ids = LevelsQuestion.all(:select => "question_id", 
        :conditions => "level_id = 15").collect(&:question_id)
Question.all(:select => "id, name", :conditions => ["id not in (?)", ids])

One shot:

Question.all(:select => "id, name",
:conditions => ["id not in (select question_id from levels_questions where level_id=15)"])

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