Editing Relational calculus (section)

{{Short description|Theory of relational databases}}
{{No footnotes|date=November 2021}}

The '''relational calculus''' consists of two calculi, the [[tuple relational calculus]] and the [[domain relational calculus]], that is part of the [[relational model]] for databases and provide a declarative way to specify database queries. The raison d'être of relational calculus is the formalization of [[query optimization]], which is finding more efficient manners to execute the same query in a database.

The relational calculus is similar to the [[relational algebra]], which is also part of the relational model: While the relational calculus is meant as a declarative language that prescribes no execution order on the subexpressions of a relational calculus expression, the [[relational algebra]] is meant as an imperative language: the sub-expressions of a relational algebraic expression are meant to be executed from left-to-right and inside-out following their nesting.

Per [[Codd's theorem]], the relational algebra and the domain-independent relational calculus are [[logical equivalence|logically equivalent]].