Question

我有一个看起来像这样的表：

有100个问题。

Table Structure for "Questions Table":

title: 
answerA:
answerB:
answerC:
answerD:
category:
difficulty:

每个问题可以有5个类别中的一个（＆＃34; 1,2,3,4或5＆＃34;）和3个难度级别中的1个（＆＃34;简单，中等或难度＆＃34; ）。

目前我按类别对其进行排序，并随机分组：

"SELECT * FROM Questions order by category, rand()";

所以现在问题按类别排序并随机化。

我希望每个类别的结果都有不同的难度级别。

这样的事情：

question 1 , category 1, difficulty easy
question 3 , category 1, difficulty medium
question 4 , category 1, difficulty hard
question 2 , category 1, difficulty easy


question 5 , category 2, difficulty easy
question 6 , category 2, difficulty medium
question 7 , category 2, difficulty hard
question 2 , category 2, difficulty easy


question 8 , category 3, difficulty easy
question 10, category 3, difficulty medium
question 9 , category 3, difficulty hard
question 0 , category 3, difficulty easy

等等。

我如何复制上述内容？我的排序似乎需要2个标准，每次为新类别打印问题时，难度标准都需要更改。

我发现的大多数Google搜索结果都与按2个字段进行分类但订单相同。

Answer 1

好。所以对于这样的订单，我们首先需要grouped rank：

(SELECT title, category, difficulty,
   @rank:=CASE 
            WHEN @category <> category OR @difficulty <> difficulty 
                 THEN 0 
            ELSE @rank+1 E
          ND AS rn,
   @difficulty = difficulty,
   @category   = category
FROM
  (SELECT @rank:= -1) s,
  (SELECT @category:= -1) c,
  (SELECT @difficulty:= -1) d,
  (SELECT *
   FROM questions
   ORDER BY category, difficulty, rand()
  ) t) as q

这为我们创建了一个表格，其中每个问题都有它在类别中的排名。现在让我们对它进行排序：

SELECT *
FROM (...) as q
ORDER BY category, rn, CASE 
                          WHEN difficulty = 'easy' 
                              THEN 1 
                          WHEN difficulty = 'medium' 
                              THEN 2
                          ELSE 3
                       END;

我的SQL顺序由2个字段组成，每次都有一个字段更改

1 个答案: