>would you not be better of making code an integer(autoinc) field?
>
>How can I do it ?
>
>if this is a multi user app is there not a (very small) risk of two people updating the table at the same time and getting the same code value ?
>
>Yes it's an application that might have up to 5 computer in a network
>Is there any risk ?

Yes, there's a huge risk, and it's no easy task to overcome. Read here for a solution: http://www.craigberntson.com/Articles/kb006.htm