I must be confused as to what you need. If you structure the Query right, and all the DB needs on that field is a customerID (primaryKey, autoincrement, generated when a customer name input on the frontend through php), and a customer name, last name, last four ssn for example, you could put almost infinite records on that db and still run a reasonably quick query to pull that data out because its only 4 field, last four (what we query by, customerID simply a fall back) is a 4 digit small int, its extremely fast to run that query. I would be happy to discuss this with you over the phone if you think that would be helpful. As it stands, you only need like 2 hours of DB work I would think, unless you want me to write the PHP & integrate it on your system, then lets say 5-6 hours.
Best,
Erik