How to Rank in MySQL Using a WHERE clause and UNION ALL

Question

I need some help with a MySQL query. I'm trying to rank participants using a WHERE clause. So, I'd like to rank novices, intermediates, and experienced separately. For example:

Rank Name    Grade  Type
----------------------------------
1    Bob     98     Novice 
2    Jill    88     Novice 
3    Jimmy   42     Novice 
1    Mark    87     Intermediate 
2    Scott   85     Intermediate
3    Jim     77     Intermediate 
1    Jane    90     Advanced 
2    John    89     Advanced 
3    Josh    87     Advanced

I've tried:

SET @rank=0;

(SELECT @rank:=@rank+1 AS rank, name, grade, type FROM myTable WHERE type='novice' ORDER BY grade DESC)
UNION ALL
(SELECT @rank:=@rank+1 AS rank, name, grade, type FROM myTable WHERE type='intermediate' ORDER BY grade DESC)
UNION ALL
(SELECT @rank:=@rank+1 AS rank, name, grade, type FROM myTable WHERE type='experienced' ORDER BY grade DESC)

I guess that I need to re-set the rank somehow. Maybe I have another problem?

Answer 1

Use:

SELECT t.name,
       t.grade,
       t.type,
       (SELECT COUNT(*)
          FROM YOUR_TABLE x
         WHERE x.type = t.type
           AND x.grade >= t.grade) AS rank
 FROM YOUR_TABLE t

To handle two grade columns, use:

SELECT t.name,
       t.grade1,
       t.grade2,
       t.type,
       (SELECT COUNT(*)
          FROM YOUR_TABLE x
         WHERE x.type = t.type
           AND (x.grade1 + x.grade2) >= (t.grade1 + t.grade2)) AS rank
 FROM YOUR_TABLE t

How would I rank the novice and intermediates together and the advanced separately?

Use:

SELECT y.*,
       (SELECT COUNT(*)
          FROM (SELECT *, 
                       CASE t.type
                         WHEN 'Advanced' THEN t.type
                         ELSE 'Non-Advanced'
                       END AS group_type
                  FROM YOUR_TABLE) x
         WHERE x.group_type = y.group_type
           AND (x.grade1 + x.grade2) >= (y.grade1 + y.grade2)) AS rank
  FROM (SELECT t.name,
               t.grade1,
               t.grade2,
               t.type,
               CASE t.type
                 WHEN 'Advanced' THEN t.type
                 ELSE 'Non-Advanced'
               END AS group_type
          FROM YOUR_TABLE t) y

Answer 2

You can do it one go, by using a more complicated ORDER BY clause.

SELECT @rank:=@rank+1 AS rank, name, grade, type 
FROM myTable 
ORDER BY 
    case type when 'novice'       then 1
              when 'intermediate' then 2 
              when 'experienced'  then 3 end,
    grade DESC
;

To make it even better, you could use a Type table to store the sort order and then add a join and then simply order by the type.sort_order then the grade, eg.

SELECT @rank:=@rank+1 AS rank, name, grade, type 
FROM myTable 
JOIN Types ON myTable.type = Types.type 
ORDER BY Types.sort_order, grade DESC;