If it's talking about primary keys (which it seems to be), it should be unique, full stop.
If it's not, where does uniqueness come in? Is it actually talking about indices, which, if I understand correctly, should have a wide spread of values (without any of them necessarily being unique) if they're to be useful?
> 1. The key should be unique to some degree.
If it's talking about primary keys (which it seems to be), it should be unique, full stop.
If it's not, where does uniqueness come in? Is it actually talking about indices, which, if I understand correctly, should have a wide spread of values (without any of them necessarily being unique) if they're to be useful?