The article by Craig Berntson at http://www.craigberntson.com/Articles/kb006.htm shows how to do that properly.

>Dear all,
>
>A multiuser-file shared incoicing system face a problem:
>
>The system have 3 machines to run, in which one machine share the datas by set exclusive off thro LAN.
>
>In every time a new invoice is generated, the application create a view of all invoicenumber order by invoicenumber, the new number is the last invoicenumber + 1.
>
>However, the problem found when two station requests the new number simultaneously, the same number generated which destory the uniqueless of the table and the system crash.
>
>In what machanism can be implemented so that the invoicenumber generation can be preform reasonably.
>
>
>
>Regards,
>
>
>Ransome