I have a form where I'm doing a lookup from the first field on a table

The form has 4 rows with the first being a ID number that is being used to lookup the rest of the data. However, some of the ID Number's do not have data in the SQL tables. What I would like to do is check if the lookup returned any SQL data for that ID Number and if so set the rest of the fields to read-only. If the lookup returns no data the fields need to be editable by the user to input that data manually.