Question

I denormalized my data (so a date is split up in a year, month, day and hour column)
But now I wonder how to query everything before a certain date.

This does NOT work:

SELECT * 
FROM  `impression_stat_hour` 
WHERE doneforday =0
AND (
    YEAR <=2011
    AND MONTH <=6
    AND DAY <=30
    AND HOUR <=1
)

This won’t actually “group” all the records together as I want them too, resulting in date that is (for example) always from hour 0 and hour 1.

Answer 1

SELECT ...
WHERE
    YEAR < 2011
    OR (YEAR = 2011 AND MONTH < 6)
    OR (YEAR = 2011 AND MONTH = 6 AND DAY < 30)
    OR (YEAR = 2011 AND MONTH = 6 AND DAY = 30 AND HOUR <= 1)

Or:

SELECT ...
WHERE STR_TO_DATE(CONCAT(year,'-',month,'-',day,' ',hour,':00:00')) <= '2011-06-30 01:00:00';

The latter is probably a lot slower (since it can’t use indexes on your various date columns. It’s also untested, since the only (ancient) version of MySQL I have access to doesn’t support STR_TO_DATE().