August 2014 Archive


Disambiguating Attributes

Sometimes we ask a query involving many relations, and among these relations are two or more attributes with the same name. If so, we need a way to indicate which of these attributes is meant by a use of their shared name. SQL solves this problem by allowing us to place a

Tuple Variables

Disambiguating attributes by prefixing the relation name works as long as the query involves combining many different relations. On the other hand, sometimes we need to ask a query that involves two or more tuples from the same relation,

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