Jinak tem dvema typum primarnich klicu se rika natural (login) a surrogate (id) keys. Na netu jsou tuny diskuzi, kde se to resi a "spravna" odpoved na to fakt neni. Ale osobne jsem pro surrogates.
Slusny je treba tohle:
http://www.agiledata.org/essays/keys.html
Fundamentally, there is no clear answer as to whether or not you should prefer natural keys over surrogate keys, regardless of what the zealots on either side of this religious argument may claim, and that your best strategy is be prepared to apply one strategy or the other whenever it makes sense.