Comments on: SQL: Ranking without self join

By: shlomi

shlomi — Thu, 13 Oct 2011 18:07:36 +0000

@Nandhagopal,
You would use something like this:
@step := IF(@prev = @curr, @step+1, 1) AS step
@rank := IF(@prev = @curr, @rank, @rank+@step) AS rank
...
SELECT @step := 1

By: Nandhagopal

Nandhagopal — Thu, 13 Oct 2011 16:42:51 +0000

I am new to the world of sql, so I apologise if my doubt sounds childish... In your examples, if two people are tied for the second spot then the one following them is 3rd. In actual conventional ranking systems, we place that fellow 4th. So, how would you change your query to incorporate it such that if m people are tied for the n'th rank, then the next person after them must be ranked (m+n).

By: Subrata

Subrata — Tue, 12 Apr 2011 09:13:04 +0000

Try this one

SELECT
s1.score_id, s1.student_name, s1.score, COUNT(DISTINCT s2.score) AS rank
FROM
score s1 JOIN score s2 ON (s1.score <= s2.score)
GROUP BY s1.score_id ORDER BY rank

By: bigcode

bigcode — Sat, 11 Dec 2010 15:36:00 +0000

I don't have an example of doing a rank without the self join but my example does allow for grouping.
http://bigcode.wordpress.com/2010/12/11/5/

By: shlomi

shlomi — Tue, 12 Oct 2010 05:32:46 +0000

@Mark, Was taught that a couple of years ago here: http://code.openark.org/blog/mysql/dynamic-sequencing-with-a-single-query#comment-63

By: Mark Plutowski

Mark Plutowski — Mon, 11 Oct 2010 20:44:47 +0000

@shlomi: thanks for the neat trick of using cross join to initialize the variables.

@GSnyder : this matters when using a tool (e.g., BI or reporting tool) that only allows entering a single SQL statement.

@Jay: as you say: "Now try your trick when you need a GROUP BY" -- Indeedy, unfort'y this is the showstopper for me too. I can't get it to work with a GROUP BY.

But hey, I still got one neat trick out of this, so thanks again for that Shlomi !

By: links for 2010-06-25 | Digitalistic - Mashup or die trying

links for 2010-06-25 | Digitalistic - Mashup or die trying — Fri, 25 Jun 2010 14:03:51 +0000

[...] SQL: Ranking without self join | code.openark.org (tags: sql join ranking optimization mysql) [...]

By: shlomi

shlomi — Tue, 02 Feb 2010 19:53:03 +0000

George,

Reset as in @c := 0, nothing fancy...

By: George

George — Tue, 02 Feb 2010 19:38:16 +0000

Hi Shlomi,

This piece of gold has already helped me immensely, thanks.

As per #18, how would I reset the other variable? I cannot seem to find anything on mysql.com

By: MySQL: Another Ranking trick « JZ Talk Blogger

MySQL: Another Ranking trick « JZ Talk Blogger — Thu, 21 Jan 2010 07:28:32 +0000

[...] Another Ranking trick I just read SQL: Ranking without self join, in which Shlomi Noach shares a nice MySQL-specific trick based on user-defined variables to [...]