Question

我正在构建一个测验应用程序，我有一个表格，其中包含属于某个类别的问题。每个类别都有自己的ID号。我无法找到一种循环遍历表格的方法，它会一次给我一个随机问题。如果有人知道可能的解决方案，请分享。谢谢！

问题控制器

class QuestionnairesController < ApplicationController

def index

    @question = Questionnaire.find(params[:category_id])
    @category = Category.find(params[:category_id])
    @videos = VideoClue.find(params[:category_id])
    ###This finds all the questions from the question table by their category_id. Whenever I select a category, it matches the question related to the category

    render :show
    ###render :show Renders Html page
end

def choose_answer

    @question = Questionnaire.find(params[:id])
    @choices = @question.choices
    #list all from the choices column

    render :choose_answer

end

def results

    @question_data= Questionnaire.where(id: params[:id])
    @correct_answer = @question_data[0].correct_answer
    @selected_answer = params[:choice]
    #In order to compare the user selected answer to the right answer, I had to make 'choice' as a param and created a variable that is equal to the params so it will render the success and error pages correctly.

    if @selected_answer == @correct_answer
        render :success
    else
        render :error
    end

显示问题页面

<style>
body {
background-color: black;
}

h1 {
color: white;
}
</style>

<center>
<img src = 'http://i.imgur.com/dz0FFLy.png' height="200" width="500" />

</center>



<center>


<br>
<br>
<h1><%=@question.question%></h1>

<br>
<br>
<br>
<br>


<form action = '/categories/<%=@category.id%>/video_clues/<%=@videos.id%>' >
<button class="btn btn-default btn-lg">Play</button>
</form>

</center>

问题表种子

     Questionnaire.create({question: "In what year did MTV (Music Television)        premiere and what was the first music video the channel aired?", choices:['1982      Michael Jackson Bille Jean', '1984 Madonna Like a virgin', '1981 The Buggles           Video Killed The Radio Star'], correct_answer:"1981 The Buggles Video Killed The      Radio Star", category_id:1})
     Questionnaire.create({question:"This game launched in 1991 on Sega Genesis which the player's mission is to collect as many golden rings as possible", choices:['Battletoads', 'Sonic The Hedgehog', 'Jewel Master'], correct_answer: "Sonic The Hedgehog", category_id:1})
     Questionnaire.create({question: "This sitcom featured four girls living under one roof. They attended the same boarding school, ran a shop together and reside in a town called Peekskill." , choices:['Designing Women', 'The Facts of Life', 'Girlfriends'], correct_answer:'The Facts of Life', category_id: 2})
     Questionnaire.create({question: "This martial arts film premiere in 1985 which featured a young man who studies Bruce Lee's techniques while on the search for his master. This was set in New York City." , choices:['The Last Dragon', 'The Karate Kid', 'Big Trouble in Little China'], correct_answer:'The Last Dragon', category_id: 3})
     Questionnaire.create({question:"This game launched in 1991 on Sega Genesis which the player's mission is to collect as many golden rings as possible", choices:['Battletoads', 'Sonic The Hedgehog', 'Jewel Master'], correct_answer: "Sonic The Hedgehog", category_id:4})

Answer 1

您可以使用窗口功能。

假设您有一个带有类别列的问题表，

select * from (
    select *,
    row_number() over (partition by "category" order by random()) as ordinal
    from questions
) X
 where ordinal = 1
;

这将从问题表中为每个类别提供一个随机行（以及额外的＆＃34;序数＆＃34; 列总是1）。它不一定特别有效。

如果问题没有那么大改变，并且上述查询实际上太慢，您可以通过使用这些总计来生成每个类别的总问题并获得特定的问题编号每个类别的随机数，然后将结果加入问题表。但首先是基准，上述情况可能足够快。

我如何在行之间循环以使用POSTGRES一次输出一个随机的“东西”？

1 个答案: