# Repetitions and permutations of columns in the semijoin algebra

ITA, pp. 179-187, 2009.

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gebouw drelational algebrasemijoin algebraprojection 1 hasselt university and transnational university of limburg agoralaanand phrases: databaseMore(4+)

Abstract:

Codd defined the relational algebra (3, 4) as the algebra with operations projection, join, restriction, union and difference. His projection operator can drop, permute and repeat columns of a relation. This permuting and repeating of columns does not really add expres- sive power to the relational algebra. Indeed, using the join operatio...More

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