When using DIS to sync data to a data source on Fliplet you want to know which currently existing records have changes that need to be synced. In most cases it will advisable for your database to have a timestamp that can be compared against. If your database does not have a timestamp you can use any other data column (that is not the primary key) to check if any records have changed and need updating.
In order to achieve this:
Change the attribute above to reference the column be it either the timestamp or any other column in your database. This will ensure that any new records are added and any existing records will be updated if there is a change detected in the column_in_database entry for that record.
Reference for DIS documentation: Data integration service | Fliplet Developers Documentation