Theory of Relational Algebra

Formal Relational Query Languages

• Relational Algebra — > Procedural and Algebra based
• Tuple Relational Calculus — → Non-Procedural and Predicate Calculus based
• Domain Relational Calculus — → Non-Procedural and Predicate Calculus based

Select Operation

The purpose is to identify, or fetch set of tuples (rows) from Relation on given conditions. General syntax: σ<condition> (Relation)

Note: there is big difference in SQL select and relation algebra select operation

Project Operation

Π <attribute> (R)

in this example project A,C from given relation .

Note : SQL select operation and relation algebra project operation is similar

but SQL select query allow duplicate values and relation algebra project dont allow duplicate values