probably more of a mysql question

Hi, I am using mysql with PHP. I have one table called inventory with an index field of: Inventory_Id int(11) NOT NULL auto_increment Now I want to create another inventory table, for a different type say Royal_Inventory where it also has a Royal_Inventory_Id int(11) NOT NULL auto_increment However, in my script I want to be able to use the two index fields as one (in another table) yet differintiate between the two Inventories. I was thinking if I could make the Royal_Inventory table have one char and then the auto-increcment value it would be a good solution; like r1 or r20012121 while inventory (not royal) would have just 1 or 20010210 . If any of you know how to do this in mysql just send me the line I need :-) It would be most appreciated. Thanks, Yoed