sql ranking with custom ties - php

Question

Hello can you help me get the rank with custom ties?
i have a table of Scores stores all the scores given by the judges.
+----+----------+-------------+--------+
| Id | judge_id |performer_id | score |
+----+----------+-------------+--------+
| 1 | 1 | 1 | 98 |
| 2 | 1 | 2 | 98 |
| 3 | 1 | 3 | 94 |
| 4 | 1 | 4 | 96 |
| 5 | 2 | 1 | 93 |
| 6 | 2 | 2 | 80 |
+----+----------+-------------+--------+
heres what the code i have searched.
SELECT
id
, judge_id
, performer_id
, score
, FIND_IN_SET(
score
, (SELECT
GROUP_CONCAT(DISTINCT score ORDER BY score DESC)
FROM
scores
WHERE
judge_id = 1
)
) AS rank
FROM
scores
WHERE
judge_id = 1
ORDER BY rank ASC
and the output of this is:
+----+----------+-------------+--------+------+
| Id | judge_id |performer_id | score | rank |
+----+----------+-------------+--------+------+
| 1 | 1 | 1 | 98 | 1 |
| 2 | 1 | 2 | 98 | 1 |
| 3 | 1 | 4 | 96 | 3 |
| 4 | 1 | 3 | 94 | 4 |
+----+----------+-------------+--------+------+
it is working but the output is not what i want.
i want to get the ranking and ties like this.
+----+----------+-------------+--------+------+
| Id | judge_id |performer_id | score | rank |
+----+----------+-------------+--------+------+
| 1 | 1 | 1 | 98 | 1.5 |
| 2 | 1 | 2 | 98 | 1.5 |
| 3 | 1 | 4 | 96 | 3 |
| 4 | 1 | 3 | 94 | 4 |
+----+----------+-------------+--------+------+
where get all the rank of the tie then divide it by how many performer ties in the rank.
ex.
performer 1 score 98 rank 1
performer 2 score 98 rank 1
suppose that performer 2 should get rank 2
i want to compute it like
1+2 = 3 then divide it by 2 since 2 performers are tie in rank 1
1=2 = 3 / 2
answer is 1.5
im sorry for my english
but please can any one help me? im stuck at this problem.

Answer 1

DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
(performer_id SERIAL PRIMARY KEY
,score INT NOT NULL
);
INSERT INTO my_table VALUES
(1,98),
(2,98),
(3,94),
(4,96);
SELECT x.*
, y.rank
FROM my_table x
JOIN
( SELECT score
, SUM(i)/COUNT(*) rank
FROM
( SELECT score
, #i:=#i+1 i
FROM my_table x
ORDER
BY score DESC
, performer_id
) a
JOIN
( SELECT #i:=0 ) vars
GROUP
BY score
) y
ON y.score = x.score;
+--------------+-------+--------+
| performer_id | score | rank |
+--------------+-------+--------+
| 1 | 98 | 1.5000 |
| 2 | 98 | 1.5000 |
| 3 | 94 | 4.0000 |
| 4 | 96 | 3.0000 |
+--------------+-------+--------+
Note: For newer versions of MySQL, you would use Windowing functions/CTE (I'm not really sure of the correct terminology). I've written this for older versions, although MySQL can have issues when initializing variables this way. If that's a problem, here's another (slightly 'hackier' - and theoretically incorrect, but practically fine) way of initialising the variable...
SELECT x.*
, y.rank
FROM my_table x
JOIN
( SELECT score
, SUM(i)/COUNT(*) rank
FROM
( SELECT score
, #j:=#j+1 i
FROM my_table x
JOIN ( SELECT #j:=0 ) vars
ORDER
BY score DESC
, performer_id
) a
GROUP
BY score
) y
ON y.score = x.score;
+--------------+-------+------+
| performer_id | score | rank |
+--------------+-------+------+
| 1 | 98 | 1.5 |
| 2 | 98 | 1.5 |
| 3 | 94 | 4 |
| 4 | 96 | 3 |
+--------------+-------+------+