Using standard mysql functions it is possible to method to write a question which will return a listing of days between two dates.
eg given 2009-01-01 and 2009-01-13 it might return a 1 column table using the values:
Edit: It seems I haven't been obvious. I wish to GENERATE this list. I've values saved within the database (by datetime) but would like them to become aggregated on the left outer join to a listing of dates as above (I'm expecting null in the right side of a number of this join for many days and can handle this).