Create incremental Ztable key

Hello everyone,

I need to create a Ztable with a key (ZID) that must be a number (like NUMC15, for example), incremented as elements are added to the table. How do i know whats the number to follow. Imagine i allready have 356 elements. So next ZID = 357.

I searched the forum and found something about number ranges. I created one. But how can i link this to my table key ?

Thank you in advance.