[Logic] Marking QSLs to print?

[logic@mailman.qth.net]

 I would like to be able to mark newly imported contest contacts for QSL label printing, but do not know the dBase commands to use to sort them the way I want.  Can anyone help?

 The criteria are to print a label for any new contact that has NOT had one printed for the same band AND mode for a previous QSO.
  So, I would like to compare all new contacts (usually from a 2-day period of a contest) to all others in the database, and if QSL_SENT=F and BAND and MODE are the same, the new contact would be marked QSL_SENT=X.  If the BAND and MODE are not the same as a previous one, set QSL_SENT=R.

  I do use the Database Command screen for other massaging of the database, but the syntax and commands to do the above requirements has escaped me so far.

  It is a real pain with 30k contacts in the log to compare all the entries in the popular countries to see if I want to print a label after a contest.
  Help!! 73 - Glenn AE0Q/V31RY