Candidate Key (1 Viewer)

[ButtonMoon]

The question arose yesterday of whether and where Microsoft document what a candidate key is. The following definition published by Microsoft seems like a perfectly OK one (with one possible quibble that in the relational model keys are supposed to be irreducible as well as uniquely identifying). So for future reference I'm posting it here rather than take the original thread off topic again.

candidate keyn.A unique identifier for a tuple (row) within a relation (database table). The candidate key may be either simple (a single attribute) or composite (two or more attributes). By definition, every relation must have at least one candidate key, but it is possible for a relation to have more than one candidate key. If there is only one candidate key, it automatically becomes the primary key for the relation. If there are multiple candidate keys, the designer must designate one as the primary key. Any candidate key that is not the designated primary key is an alternate key.See alsokey (definition 2),primary key.

Microsoft Computer Dictionary, 5th Edition, Microsoft Press

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