Time window query

I need to determine whether a date falls within a future datespan based on a given interval. For example, the division VP has several development groups, each with projects which have different review cycles (e.g. 2, 3, or 4 weeks). Based on each project begin date, he wants to know which projects are up for review during a given week. I have a generic query: select proj_begin_date from project wherebegin_date > (today - X units year) and date(windowenddate) > date(windowbegindate) and proj_begin_date < date(windowbegindate) and ((date(windowbegindate) - mod((windowbegindate) - proj_begin_date), interval) + interval) <= date(windowenddate) or mod((date(windowbegindate) - proj_begin_date),interval) = 0 or mod((date(windowenddate) - proj_begin_date),interval) = 0) Assuming: intervals are inclusive of begin/end dates X = absolute period of time windowbegindate = date of start of future date span windowenddate = date of end of future date span interval = number of days for review cycle So, for example, for a monthly (ie 30 day) review cycle and window of the first full week of February, 2001: select proj_begin_date from project whereproj_begin_date > (today - 3 units year) and date("2/5/2001") > date("2/9/2001") and proj_begin_date < date("2/5/2001") and ((date("2/5/2001") - mod((date("2/5/2001") - proj_begin_date), 30) + 30) <= date("2/9/2001") or mod((date("2/5/2001") - proj_begin_date),30) = 0 or mod((date("2/9/2001") - proj_begin_date),30) = 0 ) Are there any problems with this query? Is there a cleaner way of doing this? Is anyone aware of any repositories of date/datetime related queries that would prevent me from redundantly and repetitively reinventing the wheel over & over again?