The relational model as proposed by Codd heavily relies on Set Theory and Predicate Logic. Does SQL Server really adhere ?
closed as off topic by gbn, Mark Henderson♦ Mar 27 '11 at 1:14
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Saying that, if you want "good enough for most purposes" then yes they do. The finer points of Codd's rule and relational theory don't put food on the table, frankly. And don't metter for 99%+ of databases in the wild.