In order to delete a particular Device record in the SQL back-end you would need to do it from BT_Device table. However before attempting to delete the record from BT_Device table you need to delete any record for this device in ADM_DeviceProperty table and ADM_DeviceJob table first via DeviceID. In other words:
1. Look up deviceID for the Device within BT_Device table first
select * from bt_device where samaccountname='$samaccountname'
2. Delete any records from ADM_DeviceJOb & ADM_DeviceProperty table
delete from ADM_DeviceJob where deviceid=xxx
and
delete from ADM_DeviceProperty where deviceid=xxx
3. Now delete the device from BT_device table
delete from bt_device where deviceid=xxx
The above steps will allow for you to remove the table completely from the SQL back-end.