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Avoiding duplication of imported data

Question asked by JG on Feb 5, 2013
Latest reply on Feb 6, 2013 by JG


Avoiding duplication of imported data


     I'm sure I'm not the first person to have this issue, but I can't seem to find the right search terms to find a solution! Any help would be appreciated.

     I have three (relevant) tables: Members, Events, and Attendance. Attendance is a join table between the other two, showing which members attended which events. This is similar to the Students/Classes examples I've seen about the place.

     Data is imported to Attendance, as this is the closest match to our existing setup: we receive a list of people who attended an event, details about their profession, and the relevant event_id (the Event record will already have been created prior to receiving this info).

     The list of people attending may be a mix of people who are brand new to our client list, or who have attended previous events and will therefore already have a record in the Members table. I want to create Members records for the new people and prevent any changes from happening to the details of existing Members. 


     - list of people added to Attendance join table
     - see if they are in Members table:
     -- if so, do nothing
     -- else, add new record in Members using data from Attendance

     How do I accomplish this?