SQL group & sort by two columns [duplicate] - php

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Closed 10 years ago.
Possible Duplicate:
SQL ORDER BY total within GROUP BY
UPDATE: I've found my solution, which I've posted here. Thanks to everyone for your help!
I'm developing a Facebook application which requires a leaderboard. Scores and time taken to complete the game are recorded and these are organised by score first, then in the case of two identical scores, the time is used. If a user has played multiple times, their best score is used.
The lower the score, the better the performance in the game.
My table structure is:
id
facebook_id - (Unique Identifier for the user)
name
email
score
time - (time to complete game in seconds)
timestamp - (unix timestamp of entry)
date - (readable format of timestamp)
ip
The query I thought would work is:
SELECT *
FROM entries
ORDER BY score ASC, time ASC
GROUP BY facebook_id
The problem I'm having is in some cases it's pulling in the user's first score in the database, not their highest score. I think this is down to the GROUP BY statement. I would have thought the ORDER BY statement would have fixed this, but apparently not.
For example:
----------------------------------------------------------------------------
| ID | NAME | SCORE | TIME | TIMESTAMP | DATE | IP |
----------------------------------------------------------------------------
| 1 | Joe Bloggs | 65 | 300 | 1234567890 | XXX | XXX |
----------------------------------------------------------------------------
| 2 | Jane Doe | 72 | 280 | 1234567890 | XXX | XXX |
----------------------------------------------------------------------------
| 3 | Joe Bloggs | 55 | 285 | 1234567890 | XXX | XXX |
----------------------------------------------------------------------------
| 4 | Jane Doe | 78 | 320 | 1234567890 | XXX | XXX |
----------------------------------------------------------------------------
When I use the query above, I get the following result:
1. Joe Bloggs - 65 - 300 - (Joes First Entry, not his best entry)
2. Jane Doe - 72 - 280
I would have expected...
1. Joe Bloggs - 55 - 285 - (Joe's best entry)
2. Jane Doe - 72 - 280
It's like the Group By is ignoring the Order - and just overwriting the values.
Using MIN(score) with the group by selects the lowest score, which is correct - however it merges the time from the users first record in the database, so often returns incorrectly.
So, how can I select a user's highest score and the associated time, name, etc and order the results by score, then time?
Thanks in advance!

Answer 1

Your query does not actually make sense, because the order by should be after the group by. What SQL engine are you using? Most would give an error.
I think what you want is more like:
select e.facebookid, minscore, min(e.time) as mintime -- or do you want maxtime?
from entries e join
(select e.facebookid, min(score) as minscore
from entries e
group by facebookid
) esum
on e.facebookid = esum.facebookid and
e.score = e.minscore
group by e.facebookid, minscore
You can also do this with window functions, but that depends on your database.

Answer 2

One approach would be this:
SELECT entries.facebook_id, MIN(entries.score) AS score, MIN(entries.time) AS time
FROM entries
INNER JOIN (
SELECT facebook_id, MIN(score) AS score
FROM entries
GROUP BY facebook_id) highscores
ON highscores.facebook_id = entries.facebook_id
AND entries.score = highscores.score
GROUP BY entries.facebook_id
ORDER BY MIN(entries.score) ASC, MIN(entries.time) ASC
If you need more information from the entries table, you can then use this as a subquery, and join again on the information presented (facebook_id, score, time) to get one row per user.
You need to aggregate twice, is the crux of this; once to find the minimum score for the user, and again to find the minimum time for that user and score. You could reverse the order of the aggregation, but I would expect that this will filter most quickly and thus be most efficient.
You might also want to check which is faster, aggregating the second time: using the minimum score or grouping using the score as well.

Answer 3

You need to min the score
SELECT
facebook_id,
name,
email,
min(score) as high_score
FROM
entries
GROUP BY
facebook_id,
name,
email
ORDER BY
min(score) ASC

Answer 4

Thanks for your help. #Penguat had the closest answer.. Here was my final Query for anyone who might have the same issue...
SELECT f.facebook_id, f.name, f.score, f.time FROM
(SELECT facebook_id, name, min(score)
AS highscore FROM golf_entries
WHERE time > 0
GROUP BY facebook_id)
AS x
INNER JOIN golf_entries as f
ON f.facebook_id = x.facebook_id
AND f.score = x.highscore
ORDER BY score ASC, time ASC
Thanks again!

Answer 5

If you want their best time, you want to use the MIN() function - you said that the lower the score, the better they did.
SELECT facebook_id, MIN(score), time, name, ...
FROM entries
GROUP BY facebook_id, time, name, ...
ORDER BY score, time