>>>A primary key is unique and identifies a specific record. A candidate key is also unique, however it relates to an entity other than the primary key. An example would be a customer code, social security code, etc. If a violation of uniqueness occurs due to a duplicate – the system user must know. It has been known to have duplicate social security numbers issued. When this occurs it must be resolved. Hope you get the general concept.
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>>Thomas,
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>>PMFJI, but do you mean that if I have a uniquie control number for each record that could be the primary key, but if I also have a business need to make sure the social security number is unique, that would be a candidate? Silly question, I'm sure, but when do you need both? Why not just use the SSN?
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>>Renoir
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>Expanding on Hector's reply, in more general terms, if you want to use keys the user sees for PKs, you have to think seriously, for each and every table, what your PK will be. If you use surrogate keys (autogenerated numbers), you have a universal solution.
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>Hilmar.

Hilmar,

I actually started using a unique integer table-driven primary key for my tables not too long ago (thanks Vlad!). What's the best way to ensure uniqueness in my candidate keys?

Renoir