基于两列的Mysql排名

Question

我被困在试图找出一种方法来分配基于两个值的排名。我的表如下：

--------------------------------------- 
| id | Student | Tasks | 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 | 
--------------------------------------- 

排名值计算将错误/任务，所以我可以有最好的学生的想法，但是，约翰和RIA具有相同的排名却约翰是一个更好的学生，如他做得比利雅更多的任务，所以我需要他指派等级1 - RIA将等级2 - 短笛等级3 - 悟空等级4和贝吉塔排名5.

我试图

SELECT * from students ORDER BY Task DESC, Errors ASC 

但只按Task排序，它似乎忽略第二个值，排序rank会好的，但那我该如何分配正确的订单？

要分配的新rank应该基于最大任务数量。最少的错误数量，因此具有更多任务和更少错误的学生应该位于第1位，依此类推。

Answer 1

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

如果您没有，叔具有rank（Errors/Tasks）柱然后;

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

如果你只想order您的结果，那么，

order by `Rank` asc, `Tasks` desc 

的

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

编辑 如果一个新的用户只有20任务和0误差

？

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

Answer 2

使用您计算在ORDER BY

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

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]>