>I want to have a auto-number field in the multi-user environment.
>I frequently use table buffering in my input forms.
>How to eliminate duplicate key when inputting ?

I do it this way:

1. I use INTEGER keys wherever possible.

2. I have a table (LASTKEY) with just one record, holding (surprise!) the last used key number.

3. I wrote a function (GETNEXTKEY) which opens LASTKEY EXCLUSIVEly, increments the last key number, and returns that value. (Don't forget to close the table, or you will cause quite a deadlock!)

4. I specify GETNEXTKEY() as the default value for all key fields.

Note: it's OK to share the same LASTKEY for all tables, since with INTEGER fields you have more than 2 billion possible key values, and that allows me not to worry about unused key values either. (If the user starts to insert a new record but cancels it, a key value will go unused. So what?)