Update the rank in a MySQL Table - mysql

Question

I have the following table structure for a table Player
Table Player {
Long playerID;
Long points;
Long rank;
}
Assuming that the playerID and the points have valid values, can I update the rank for all the players based on the number of points in a single query? If two people have the same number of points, they should tie for the rank.
UPDATE:
I'm using hibernate using the query suggested as a native query. Hibernate does not like using variables, especially the ':'. Does anyone know of any workarounds? Either by not using variables or working around hibernate's limitation in this case by using HQL?

Answer 1

One option is to use a ranking variable, such as the following:
UPDATE player
JOIN (SELECT p.playerID,
#curRank := #curRank + 1 AS rank
FROM player p
JOIN (SELECT #curRank := 0) r
ORDER BY p.points DESC
) ranks ON (ranks.playerID = player.playerID)
SET player.rank = ranks.rank;
The JOIN (SELECT #curRank := 0) part allows the variable initialization without requiring a separate SET command.
Further reading on this topic:
SQL: Ranking without self join
Stack Overflow: Create a Cumulative Sum Column in MySQL
Test Case:
CREATE TABLE player (
playerID int,
points int,
rank int
);
INSERT INTO player VALUES (1, 150, NULL);
INSERT INTO player VALUES (2, 100, NULL);
INSERT INTO player VALUES (3, 250, NULL);
INSERT INTO player VALUES (4, 200, NULL);
INSERT INTO player VALUES (5, 175, NULL);
UPDATE player
JOIN (SELECT p.playerID,
#curRank := #curRank + 1 AS rank
FROM player p
JOIN (SELECT #curRank := 0) r
ORDER BY p.points DESC
) ranks ON (ranks.playerID = player.playerID)
SET player.rank = ranks.rank;
Result:
SELECT * FROM player ORDER BY rank;
+----------+--------+------+
| playerID | points | rank |
+----------+--------+------+
| 3 | 250 | 1 |
| 4 | 200 | 2 |
| 5 | 175 | 3 |
| 1 | 150 | 4 |
| 2 | 100 | 5 |
+----------+--------+------+
5 rows in set (0.00 sec)
UPDATE: Just noticed the that you require ties to share the same rank. This is a bit tricky, but can be solved with even more variables:
UPDATE player
JOIN (SELECT p.playerID,
IF(#lastPoint <> p.points,
#curRank := #curRank + 1,
#curRank) AS rank,
#lastPoint := p.points
FROM player p
JOIN (SELECT #curRank := 0, #lastPoint := 0) r
ORDER BY p.points DESC
) ranks ON (ranks.playerID = player.playerID)
SET player.rank = ranks.rank;
For a test case, let's add another player with 175 points:
INSERT INTO player VALUES (6, 175, NULL);
Result:
SELECT * FROM player ORDER BY rank;
+----------+--------+------+
| playerID | points | rank |
+----------+--------+------+
| 3 | 250 | 1 |
| 4 | 200 | 2 |
| 5 | 175 | 3 |
| 6 | 175 | 3 |
| 1 | 150 | 4 |
| 2 | 100 | 5 |
+----------+--------+------+
6 rows in set (0.00 sec)
And if you require the rank to skip a place in case of a tie, you can add another IF condition:
UPDATE player
JOIN (SELECT p.playerID,
IF(#lastPoint <> p.points,
#curRank := #curRank + 1,
#curRank) AS rank,
IF(#lastPoint = p.points,
#curRank := #curRank + 1,
#curRank),
#lastPoint := p.points
FROM player p
JOIN (SELECT #curRank := 0, #lastPoint := 0) r
ORDER BY p.points DESC
) ranks ON (ranks.playerID = player.playerID)
SET player.rank = ranks.rank;
Result:
SELECT * FROM player ORDER BY rank;
+----------+--------+------+
| playerID | points | rank |
+----------+--------+------+
| 3 | 250 | 1 |
| 4 | 200 | 2 |
| 5 | 175 | 3 |
| 6 | 175 | 3 |
| 1 | 150 | 5 |
| 2 | 100 | 6 |
+----------+--------+------+
6 rows in set (0.00 sec)
Note: Please consider that the queries I am suggesting could be simplified further.

Answer 2

Daniel, you have very nice solution. Except one point - the tie case. If tie happens between 3 players this update doesn't work properly. I changed your solution as following:
UPDATE player
JOIN (SELECT p.playerID,
IF(#lastPoint <> p.points,
#curRank := #curRank + #nextrank,
#curRank) AS rank,
IF(#lastPoint = p.points,
#nextrank := #nextrank + 1,
#nextrank := 1),
#lastPoint := p.points
FROM player p
JOIN (SELECT #curRank := 0, #lastPoint := 0, #nextrank := 1) r
ORDER BY p.points DESC
) ranks ON (ranks.playerID = player.playerID)
SET player.rank = ranks.rank;

Answer 3

EDIT: The update statement presented earlier did not work.
Although this is not exactly what you are asking for: You can generate the rank on the fly when selecting:
select p1.playerID, p1.points, (1 + (
select count(playerID)
from Player p2
where p2.points > p1.points
)) as rank
from Player p1
order by points desc
EDIT: Trying the UPDATE statement once more. How about a temporary table:
create temporary table PlayerRank
as select p1.playerID, (1 + (select count(playerID)
from Player p2
where p2.points > p1.points
)) as rank
from Player p1;
update Player p set rank = (select rank from PlayerRank r
where r.playerID = p.playerID);
drop table PlayerRank;
Hope this helps.

Answer 4

According to Normalization rules, rank should be evaluated at SELECT time.