I see what you're saying, it's probably that I've written systems where duplicated SSN's were far more common than they should be and it was WANTED to allow them to...

David Portas (11/4/2010)

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Ultimately any key value (including a surrogate) can change but what makes keys useful and important is the fact that the database enforces their uniqueness and that therefore...

That's what I don't get, an SSN doesn't uniquely identify a person. I've seen duplicates, missing data, or it's wrong. Is it an attribute of an entity? Aye....

In what way out of curiosity?

SSN's keep being mentioned, but they can change/be missed/be duplicates. Most other 'natural' keys end up falling to the same traps. Therefore, they're...

No, though I did enjoy that series of posts he made. When I ask people to read that stuff, I do wonder where he is now though. Pity...

Aye. Never had problems merging DB's. That's why GUID's are so excellent and why I refer people to Quazibubble's posts.

http://www.sqlteam.com/Forums/topic.asp?TOPIC_ID=6136&whichpage=3

He does a far better job explaining this...

I'd love to enforce the uniqueness, but that it isn't unique and can change shows there's an issue with using it. There may be that case where it's valid...

Hugo Kornelis (10/25/2010)

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If by "Just use a PK and you'll not worry", you mean use a surrogate key as the primary key and no UNIQUE constraint on the SSN, then...

ebay-1087924 (10/25/2010)

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Consider a people list originally keyed by SSN. Replacing SSN with a surrogate key means that -- unless you add a secondary uniqueness constraint -- you can then...

Totally! Sure, it takes a bit of time to get the good stuff out, but everything...

Read;

http://www.sqlteam.com/forums/topic.asp?TOPIC_ID=6136&whichpage=2

All of quazibubble's posts, including his...

Anytime this gets brought up (and it does, time and time again), before we argue further, I /really/ recommend reading;

http://www.sqlteam.com/forums/topic.asp?TOPIC_ID=6136&whichpage=2

and quazibubble's posts. Yes he's argumentative, but puts...