• Relational Algebra is a theoretical foundation for the query languages(SQL) used in relational database management systems (RDBMS).


  • Relational algebra is a formal system used to manipulate relations (tables) in relational databases.


  • Relational algebra provides a foundation for expressing queries and transformations on relational databases.
  • It’s a mathematical framework that helps in understanding and designing efficient database queries and operations.

Relational Algebra Operations

The common operations used in relational algebra are:-

  • Selection (σ):
    • This operation retrieves rows from a relation/table that satisfy a given condition.
    • It’s analogous to the WHERE clause in SQL.
  • Projection (π):
    • This operation retrieves specific columns from a relation, discarding the rest.
    • It’s similar to the SELECT clause in SQL.
  • Union (∪):
    • This operation combines tuples from two relations(tables) that have the same schema, removing duplicates.
  • Intersection (∩):
    • This operation returns tuples that exist in both of the two relations.
  • Difference (-):
    • This operation returns tuples that are in one relation but not in the other.
  • Cartesian Product (×):
    • This operation combines every tuple in one relation with every tuple in another relation, resulting in a new relation with combined tuples.
  • Join (⨝):
    • This operation combines tuples from two relations based on a common attribute, creating a new relation.
    • There are various types of joins, such as inner join, outer join (left, right, full), and natural join.


Categories: DBMS


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