Question

I’m really struggling creating a select statement that will return the record with the fastest time for each user.
If there is a tie on number if seconds, the lowest ‘clicks’ should be selected.

If I have the following records in my table

user    seconds     clicks
1       10.23       10
1       10.12       12
1       10.12       14
2       12.11       16
3       12.34       18
3       12.00       16

I need the lowest time and clicks for each user, so I need a query to return

user    seconds    clicks
1       10.12       12
2       12.11       16
3       12.00       16

The query I’ve tried is

select user, min(seconds), min(clicks) from mytable group by user

But it selects seconds 10.12 and clicks 10 for user 1 which is incorrect.
Can I do this in 1 query?

Answer 1

This is a variation of the greatest-n-per-group problem that comes up frequently.

SELECT m.*
FROM mytable AS m
LEFT OUTER JOIN mytable AS m2 ON m.user = m2.user
  AND (m.seconds > m2.seconds OR m.seconds = m2.seconds AND m.clicks > m2.clicks)
WHERE m2.user IS NULL;

Explanation:

We want m to be the row for each user that has the lowest seconds, or if there’s a tie for lowest seconds, the lowest clicks. In other words, there should be no other row for that user with a lower seconds or a lower clicks.

Use an exclusion join trying to find any row with lower seconds or lower clicks. If no such row is found, then m is the one with the lowest values.

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It’s still possible to result in a tie and return more than one row for a user, if there’s more than one row with the least seconds and least clicks. In that case, you need to resolve the tie with some other column, hopefully one that is unique.

Example:

SELECT m.*
FROM mytable AS m
LEFT OUTER JOIN mytable AS m2 ON m.user = m2.user
  AND (m.seconds > m2.seconds OR m.seconds = m2.seconds AND (m.clicks > m2.clicks
  OR m.clicks = m2.clicks AND m.id > m2.id))
WHERE m2.user IS NULL;