Auto Populate Column In SQL

Question

I Have 2 Columns

1. IDnumber
2. User Name

IDnumber is set to Auto_Increment So that it will be filled automatically starting from 10000 when a data is added I want to Auto populate the column Username by concatenating IDnumber and word @BA

So that When the IDnumber autoincrement is 10006 the User Name Will be 10006@BA

I want to do this in my SQL Data Base

• The other data in the database is being filled using a PHP form