Assign a registration no. automatically on filling a form

Hi Everybody, I have built a registration form for an application, where users have to provide their Name, City, Region and Date of Birth which are then saved ito a database table.Now I want to make an application which enables me to immediately allot unique registration no. to the registered users on filling up the form.The registration no must be comprised of the Initial name of the user, Region name initials(Region name initials present in the database) , date of birth of the user and a counter no(the counter increases when user of a particular region gets registered) . And finally the Registration No is saved to the database table containing user data.

Can anybody help me with some code ar give an idea to do it?

 

Thnks in advance........
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