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Message: <blockquote data-quote="Anthony Vaughan" data-source="post: 1269372" data-attributes="member: 153283">I have given you samples of code doing it both ways and why only a unique ID will work. My method avoids having to compare every record in the source table to see whether it exists in the target table. This matters when there are thousands of records. I have developed commercial systems involving tens of millions of records and this design allows data to be accessed and retrieved in less than a second. SQLite is not an enterprise database so addressing performance, and using every trick possible, is even more important.I would be very happy to hear, in detail, how using a compound key could achieve what we my code does; i.e. only writing new data to the target table without having to read any records in the target table first.Tony</blockquote>