在分组和在php中排名时遇到问题

Question

Am issues with grouping and rank in php i don;t know if my entire code is wrong but have been able to group it and rank but the ranking is not correct Here is my code

SELECT g1.regnumber, g1.subject_id , g1.score , COUNT(*) AS rank
FROM tbl_result AS g1 JOIN
     tbl_result AS g2
     ON (g2.score, g2.regnumber) >= (g1.score, g1.regnumber) AND
        g1.subject_id = g2.subject_id
 WHERE g2.subject_id='11'
 GROUP BY g1.regnumber, g1.subject_id , g1.score
 ORDER BY g1.subject_id , rank

Here is the result

regnumber   subject_id   score   Rank   
0217            11         89      1
0200            11         78      2
2021            11         50      3
7737            11         200     4
0917            11         100     5

Which is not correct

Don't mind my code, all i need is a sql code that can group and rank also using where clause. Thanks.

Answer 1

Your problem would appear to be storing the score as a string rather than a number. You can fix the query. But I would go to the root cause and fix the problem by doing:

alter table modify column score int;

I do think the query is a bit cumbersome. I would be more inclined to write it using a correlated subquery or using variables. The latter is pretty simple:

SELECT tr.regnumber, tr.subject_id, tr.score,
       (@rn := @rn + 1) as rank
FROM (SELECT tr.*,
      FROM tbl_result tr
      WHERE g1.adnumber = 'ctydemo' AND g2.subject_id = 11
      ORDER BY tr.score DESC, tr.regnumber DESC
     ) tr CROSS JOIN
     (SELECT @rn := 0) params
ORDER BY tr.subject_id, rank;

Note: This assumes that the type of score is fixed. It is easy enough to adjust the query by doing:

ORDER BY (tr.score + 0) DESC, tr.regnumber DESC

Answer 2

seems that your score is a string

in this case if you don't want change the struct of your table you can try cast your score column from string to int

  SELECT g1.regnumber, g1.subject_id , g1.score , COUNT(*) AS rank
  FROM tbl_result AS g1 JOIN
       tbl_result AS g2
       ON (cast(g2.score as integer), g2.regnumber) >= (cast(g1.score as integer), g1.regnumber) AND
          g1.subject_id = g2.subject_id
   WHERE g2.subject_id='11'
   GROUP BY g1.regnumber, g1.subject_id , g1.score
   ORDER BY g1.subject_id , rank