Natural Join (Relational Algebra)

relational-algebra

Definition

Natural Join (Relational Algebra)

The natural join combines two relations via common attributes (same names and domains) by combining only tuples with the same values for common attributes.

Given two relations and , the natural join can be expressed using projection, selection and the Cartesian Product:

Example

Given two relations and :

Students Relation:

StudentID	Name	Major
S101	Alice	Physics
S102	Bob	CS
S103	Charlie	Biology

Enrolments Relation:

StudentID	CourseID	Grade
S101	C22	A
S102	C15	B
S102	C22	A
S104	C15	C

There’s only one common attribute, namely StudentID. Therefore, the join condition is:

Thus, the resulting relation is:

StudentID	Name	Major	CourseID	Grade
S101	Alice	Physics	C22	A
S102	Bob	CS	C15	B
S102	Bob	CS	C22	A