基于两列

Question

我试图想出一种基于两个值来分配排名的方法。我的表格如下：

---------------------------------------
| id | Student | Tasks | Errors | Rank |
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| 1  | Vegeta  | 80    | 1500   | 18.7 |
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| 2  | Ria     | 100   | 150    | 1.5  |
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| 3  | John    | 200   | 300    | 1.5  |
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| 4  | Goku    | 24    | 100    | 4.16 |
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| 5  | Piccolo | 80    | 148    | 1.85 |
---------------------------------------

排名值是根据错误/任务计算出来的，所以我可以了解最好的学生，但是，约翰和里亚有相同的等级，但约翰是一个更好的学生，因为他做了比Ria更多的任务，所以我需要指定他排名1 - ria将排名2 - Piccolo排名3 - 悟空排名4和Vegeta排名5.

我试过

SELECT * from students ORDER BY Task DESC, Errors ASC

但只按Task对其进行排序，似乎忽略了第二个值，按rank排序就可以，但是我可以如何分配正确的顺序？

要分配的新rank应基于任务Vs的最大数量。最小错误数，因此具有更多任务和更少错误的学生应该在等级1上，依此类推。

Answer 1

在 ORDER BY

中使用您的计算

SELECT * from students
ORDER BY (Errors / Task), Task DESC;

<强>结果：

MariaDB [test]> select * from students;
+----+---------+------+--------+------+
| id | Student | Task | Errors | Rank |
+----+---------+------+--------+------+
|  1 | Vegeta  |   80 |   1500 | 18.7 |
|  2 | Ria     |  100 |    150 |  1.5 |
|  3 | John    |  200 |    300 |  1.5 |
|  4 | Goku    |   24 |    100 | 4.16 |
|  5 | Piccolo |   80 |    148 | 1.85 |
+----+---------+------+--------+------+
5 rows in set (0.00 sec)

MariaDB [test]>
MariaDB [test]> SELECT * FROM students
    -> ORDER BY (ERRORS / Task), Task DESC;
+----+---------+------+--------+------+
| id | Student | Task | Errors | Rank |
+----+---------+------+--------+------+
|  3 | John    |  200 |    300 |  1.5 |
|  2 | Ria     |  100 |    150 |  1.5 |
|  5 | Piccolo |   80 |    148 | 1.85 |
|  4 | Goku    |   24 |    100 | 4.16 |
|  1 | Vegeta  |   80 |   1500 | 18.7 |
+----+---------+------+--------+------+
5 rows in set (0.00 sec)

MariaDB [test]>

Answer 2

试试这个;

select t.*, @r := @r + 1 as `new_rank`
from  tbl t,
(select @r := 0) r
order by `Rank` asc, `Tasks` desc

演示 sqlfiddle

如果你没有，那么就有rank（Errors / Tasks）列;

select 
  `id`, `Student`, `Tasks`, `Errors`,
  @r := @r + 1 as `rank`
from  tbl t,
(select @r := 0) r
order by (`Errors` / `Tasks`) asc, `Tasks` desc

sqlfiddle

如果您只想order您的结果;

order by `Rank` asc, `Tasks` desc

的

order by (`Errors` / `Tasks`) asc, `Tasks` desc

修改 如果新用户只有20个任务且0个错误？

select t.*, @r := @r + 1 as `new_rank`
from  tbl t,
(select @r := 0) r
order by 
  case when `rank` = 0 then 0 else 1 end desc, 
  `Rank` asc, `Tasks` desc

sqlfiddle