Table of Contents## Relational Algebra and Relational Calculus

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The most common algebraic query language is called the
*relational algebra*. This language is
*procedural* , in the sense that its expressions actually describe an
explicit procedure for returning the results. Languages that use logic
fall under the heading of the *relational calculus*
(there is more than one such language in common use).
These languages are *nonprocedural* , since their expressions represent statements that
describe conditions that must be met for a row to be in the result
table, without showing how to actually obtain those rows.

Let us illustrate these ideas with an example. Consider the following request, written in plain English: