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For questions about the algebra of relational model theory, involving operations like Projection (π) Selection (σ), Rename (ρ), and Natural join (⋈).

Relational algebra, first created by Edgar F. Codd while at IBM, is a family of algebras with a well-founded semantics used for modelling the data stored in relational databases, and defining queries on it.

The main application of relational algebra is providing a theoretical foundation for relational databases, particularly query languages for such databases, chief among which is SQL.

The five basic operators of Codd's algebra are:

  • selection
  • projection
  • Cartesian product
  • set union
  • set difference