Yeah, I couldn't think of a better subject line.
Basically, I have a membership table that lists each member with an effective period, Eff_Period, that indicates a month when a member was active. So, if a member is active from Jan to Mar, there will be three rows with Eff_Periods of 201501, 201502 and 201503.
All well and good.
But, a member may not necessarily have continuous months for active membership. They might have only been active for Jan, Feb and Jun. That would still give them three rows, but with noncontinuous Eff_Periods; they'd be 201501, 201502 and 201506.
There is also a table that logs member activity. It has an Activity_Date that holds the date of the activity - betcha didn't see that comin'. What I'm trying to do is determine if an activity took place during a period when the member was active.
My original thought was to count how many rows a member has in the Membership table and compare that number to the number of months between the MIN(Eff_Period) and the MAX(Eff_Period). If the numbers didn't matchup, then I knew that the member had a disconnect somewhere; he became inactive, then active again. But, then I thought of the scenario I detailed above and realized that the counts could match, but still have a discontinuity.
So, is there a nifty little SQL shortcut that could determine if a target month is contained within a continuous or discontinuous list of months?
Thanx in advance!