How to add autoincrement field

[Proware]

I want to add an autoincrement field to the Contacts table. This will be used as a unique reference to assign users for them to register on a landing page I am developing.

The ID field is already a Primary key and so MYSQL will not allow me to create a new Autoincrement field.

How can I implement such a field?

[ruchida]

How about creating a custom field of int type, and then change it to an unique key?

[Proware]

Wont this then clash with id_c in contacts_ctsm which is the primary key?

[ruchida]

You don't need to set the custom field a primary key, but you can only set it an unique key.