Extract Data from a SQL database into Quickbase fields?

If you add a web service to your SQL database, then you can use AJAX to retrieve the data. Jquery can grab the account number from the value field in the QB form and add it to a request. Then use AJAX to retrieve the data from the web service and push to QB via QB API or push the data directly to fields on the form via js. If you use the image on load technique, you can add an event listener that executes the js when the account number field is not blank.
This is just a general overview, but it is possible.