[panda17]

In general there can be more than one candidate key for a given relation (table). Only one candidate key is "primary", all others are "alternate".

[mulmen]

Thanks that makes sense.

Is this an industry term or are you just using it here to emphasize the difference?

[dspillett]

I've seen alternate used in other places to refer to candidate keys that are not currently the primary key, though I'm fairly sure it isn't a defined standard term.

[marcos100]

Industry term. But it is usually unknown to people who tend to use id as primary key for every table.

[mulmen]

Do you mean synthetic keys rather than natural keys?