Relational algebra is a procedural query language that provides a theoretical foundation for relational databases and SQL. It uses algebraic structures to model data and define queries on it with a well-founded semantics. The main purpose of relational algebra is to define operators that transform one or more input relations into an output relation. These operators accept relations as input and produce relations as output, and they can be combined and used to express potentially complex queries that transform potentially many input relations into a single output relation. The fundamental operations of relational algebra include:

• Select: This operation is used to select a subset of tuples from a relation that satisfy a given condition.

• Project: This operation is used to select a subset of attributes from a relation.

• Union: This operation combines two relations and eliminates duplicates.

• Intersection: This operation returns only the tuples that are common to both relations.

• Difference: This operation returns only the tuples that are in one relation but not the other.

• Cartesian product: This operation returns all possible combinations of tuples from two relations.

• Rename: This operation is used to rename the output relation.

Relational algebra is a procedural query language, which means it gives a step-by-step process to obtain the result of the query. It is different from relational calculus, which is a non-procedural query language that tells what to do but not how to do it.