Relational Query Languages

• Query languages: Allow manipulation and retrieval of data from a database
• Types
  • SQL
    • A declarative language because you write what you want instead of how to get it
  • Relational Algebra
    • Mathematical expression (procedural)
    • Useful for representing execution plans
  • Relational Calculus
    • Declarative mathematics
    • Not covered
• A query is applied to relation instances and the result of a query is also a relation instance
  • Schemas of input and output relations for a query are determined by query
• Since each operation returns a relation, operations can be composed (the algebra is closed)