Hi there, @lordcortes… just for kicks (my own, of course), I created an example that is pretty much (if not exactly) what Ghost described, and I will share some screenshots so you can use them as a reference. But first, be aware that the unique letter/number combinations might not be unique if users select numbers at the same time. If you want to learn more about that (and you should), read this post, and while you’re at it, read the entire thread.
The above being said, I started my example by creating a data type called User Unique Num. I created two options sets, one for the numbers called OS Numbers and one for the letters called OS Letters, and I added an attribute called number (of type number) to the letters option set so I could give each letter a corresponding number (1 through 26, obviously). With the option sets in place, I created two fields in the User Unique Num data type… a field called number that links to the numbers option set and a field called letter that links to the letters option set.
Next, I added a dropdown to the page that displays the options from the numbers option set, and I added a button that creates a thing in the User Unique Num data type. There are two workflow events associated with the button, and the first one looks like this.
That event will always assign the letter A when the number selected in the dropdown hasn’t already been used. The second workflow event looks like this.
That event will find the last thing in the User Unique Num data type that has the same number as the number selected in the dropdown, and then it gets the letter that is after that thing’s letter. Note that the searches on the workflow event and the list filter have the same constraint as shown in the first screenshot.
Anyway, I tested those workflows, and they do exactly what you described, but again, the letter/number combinations might not always be unique unless you combine what I have shown with the information in the linked post.
Hope this helps.
Best…
Mike