Has anyone solved this with a plugin? I have been reading 122 pages of plugins. So far no luck.

The issue is that I need to have at least one field that is unique and one a field that is auto incrementing.

I need basically a Serial text field that is unique and an auto-generated membership number.

Desired solution:

1. User registers and is prompted with a field
user enters a unique text field (10 chars or so). If the field is unique in the database, then they are allowed to register; if not they are prompted to fill out the field again (or back to registration)

2. After that is accepted, an auto-generated membership number is populated into a custom field.

This would be extremely useful. Membership #'s would be a great example.
Upon safe, if the value is null, the next member # gets inserted.
If anyone has a solution, please share. Thanks a lot