如何在MySQL中根据其他列自动更新表的列？

Question

In my table, in one hour, 50 students will submit their marks in some exam everyday.

Following is the table

ID    StudID  Marks  Rank
1     101     56 
2     102     23
3     103     84
4     104     96
5     105     44

I want when all these records are inserted, the rank should get auto calculated and get insterted against each record. For example, Rank column will get filled like this:

ID    StudID  Marks  Rank
1     101     56     3
2     102     23     5
3     103     84     2
4     104     96     1
5     105     44     4

I want to create a single query for this in mysql. Would it be done in a single query or will it require any functions or procedure? How should I write query, function or procedure for above logic in mysql?

Note: I have to implement above logic using PHP.

Answer 1

UPDATE  TableName a
        INNER JOIN
        (
          SELECT  StudID, Marks,
                 (SELECT    COUNT(DISTINCT b.Marks) 
                  FROM  tableName b
                  WHERE a.Marks <= b.Marks
                  ) as rank
          FROM    tableName a
          ORDER   BY Marks DESC
          ) b ON a.StudID = b.StudID
SET a.Rank = b.rank

• SQLFiddle Demo

Answer 2

I assuming the student rerun the insert query, so when the student submit their mark they run query insert into ... Try this:

INSERT INTO <thetable> (ID, StudID, Marks, Rank)
VALUES (<theid>, <thestudentid>, <themark>, NULL)
ON DUPLICATE KEY UPDATE Rank = (SELECT COUNT(*)+1
                                  FROM <thetable>
                                 WHERE Rank IS NOT NULL);

Another assumption: initial value for column "Rank" is NULL , or if empty string change the condition Rank IS NOT NULL to Rank = ''