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Learning PostgreSQL by Andrey Volkov, Achim Vannahme, Salahaldin Juba

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Relational algebra

Relational algebra is the formal language of the relational model. It defines a set of closed operations over relations, that is, the result of each operation is a new relation. Relational algebra inherits many operators from set algebra. Relational algebra operations could be categorized into two groups:

  • The first one is a group of operations which are inherited from set theory such as UNION, INTERSECTION, SET DIFFERENCE, and CARTESIAN PRODUCT, also known as CROSS PRODUCT.
  • The second is a group of operations which are specific to the relational model such as SELECT and PROJECT.

Relational algebra operations could also be classified as binary and unary operations. Primitive relational algebra operators have ultimate power of reconstructing ...

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