<< Next, I used a UNION: SELECT idnum FROM active UNION SELECT idnum FROM inactive
That gave me the results I was looking for. I thought that the UNION statement above was equal to the FULL OUTER JOIN. Have I misunderstood how the FULL OUTER JOIN works? >> Yes and no. The SELECT UNION solution is correct. I think you may be getting confused by two different uses of the word UNION in R:Base. The old UNION _statement_ would produce a new table by JOINing to other tables together. The UNION statement and the SELECT OUTER JOIN are very similar (UNION would produce a permanent table while SELECT OUTER JOIN produces a transient dataset) I think this is what you're thinking of. Since the introduction of VIEWs into R:Base, this UNION statement has been pretty much unecessary. The SELECT UNION syntax is actually quite different from the old UNION statement and from a SELECT JOIN statement. SELECT JOIN (and the old UNION statement) both produce output that is _wider_ (joined together horizontally, if you want to think of it that way). But the SELECT UNION statement produces output that is _taller_ (joined together vertically). -- Larry
