I have a Table "password" in Oracle.I created 2 text box in Vb and 2 label box(UserName,Password) and 2 command button(Ok, Cancel).

I want to store that values in Oracle Backend.I created a table "Password" in Oracle and i created a primary key to username.Ok...


But when i click the ok button, it should give a message that "This user already exists.Please type another name".
How it can be done...?
Please this time don't suggest any topic but write code if u know..please

Thanks In advance