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5. Query Languages and the Relational Al... > 5.2. Relational Algebra and Relation...

Relational Algebra and Relational Calculus

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:


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