Question

I have a table:

  id | score | date
 bob |    40 | 2010-1-1
 bob |    70 | 2010-1-15
 sue |    55 | 2010-1-1
 sue |    80 | 2010-2-1

I want to query for either the score for a user on a specific date OR, if no score exists for that user on that date,return the score from the most recent date for that user.

Is there a way to do this without a sub-query?

For instance, if I do:

SELECT score
FROM table
WHERE id = '$id'
AND IFNULL(
    date = DATE(FROM_UNIXTIME($date)),
    MAX(date)   
    )

I would get no result, as the id does not show up for the most recent date.

Update

Felix reminded me I can’t use aggregate functions in the WHERE clause, so now I’m wondering if there is a pseudo-aggregate date function for saying “most recent date” in the where clause, and if so, if I can specify the user when using THAT function?

Update 2

So this is what I have gotten to work, but I still don’t know if it’s the best way to go (ie, do I need the nested query?):

SELECT score
FROM table
WHERE id = '$id'
AND date = IFNULL(
    (SELECT date FROM table
    WHERE id = '$id' AND
    date = DATE(FROM_UNIXTIME($date))
    ),
    (SELECT MAX(date) FROM table
    WHERE id = '$id'
    )
)

Answer 1

Not sure of the performance of this one:

SELECT a.*
FROM table a
LEFT JOIN table b ON (
  b.date=DATE(FROM_UNIXTIME($date)) AND b.date=a.date AND b.id=a.id
)
WHERE a.id='$id'
ORDER BY b.date DESC, a.date DESC
LIMIT 1