I have an old database and a new database. The old records were converted to the new database recently. All our old applications continue to point to the old database, but the new applications point to the new database.

Currently the old database is the only one being updated, so throughout the day the new database becomes out of sync. It is acceptable for the new database to be out of sync for a day, so until all our applications are pointed to the new database I just need to write a nightly cron job that will bring it up to date.

I do not want to purge the new database and run the complete conversion script each night, as that would reduce uptime and would create a mess in our auditing of that table.

I'm thinking about selecting all the data from the old database, converting it to the new database structure in memory, and then checking for the existence of each record before inserting it in the new database. After that's done, I'd select everything from the new database and check if it exists in the old one, and if not delete it.

Is this the simplest way to do this?