MySQL：基于外部行的范围 table

Question

我正在使用 MySQL 来解决这个问题。我需要根据用户在某个问题上花费的总时间来给用户打分。我计算了用户花费的时间。假设它在 user_time table.

user_id    question_id time_spent
      1         1         7
      1         2         50
      2         1         11

我的积分是基于范围的：

[0-10) seconds: 100 points, 
[10-20) seconds: 300 points, 
[20-30) seconds: 500 points, 
[30, inf): 1000 points

准确的 10 秒将给我 300 分。不过，鉴于我是根据系统时钟差异计算的，确切数字的变化会很低。

此信息目前在外部评分tablepoints_table

time_spent points
0          100
10         300
20         500
30         1000

我需要一个查询来找出秒属于哪个范围并给我那个结果。

user_id question_id points
1       1           100
1       2           1000
2       1           300

我尝试考虑不同类型的联接，但想不出一种可以满足这一特定要求的联接。

Answer 1

我认为最简单的方法是相关子查询。像这样：

select ut.*,
       (select pt.points
        from points_table pt
        where pt.time_spent <= ut.time_spent
        order by pt.time_spent desc
        limit 1
       ) as points
from user_time ut

Answer 2

试试这个：

SELECT ut.user_id, ut.time_spent, A.points 
FROM user_time ut 
INNER JOIN (SELECT p1.time_spent AS time_spent1, 
                   p2.time_spent AS time_spent2, 
                   p1.points 
            FROM points_table p1 
            INNER JOIN points_table p2 ON p1.time_spent < p2.time_spent 
            GROUP BY p1.time_spent
           ) AS A ON ut.time_spent BETWEEN A.time_spent1 AND A.time_spent2

Answer 3

换个角度看，你可以在没有分数的情况下获得相同的结果table:

SELECT *,
  CASE
    WHEN time_spent >= 30 THEN 1000
    WHEN time_spent >= 20 THEN 500
    WHEN time_spent >= 10 THEN 300
    ELSE 100
  END 'Points'
FROM user_time;

MySQL：基于外部行的范围 table

MySQL: Range based on rows in external table

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