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Traditional set operators in Relational Database Model

The union of two relations A and B is the set of all tuples belonging to either A or B (or both).

Example:

A = The set of employees whose department is S/W Development
B = The set of employee whose age is less than 30 years.
A UNION B = The set of employees whose are either in S/W development department or having age less than 30 years.

Intersection:

The intersection of two relations A and B is the set of all tuples t belonging to both A and B.

Example:

A = The set of employees whose department is S/W Development
B = The set of employee whose age is less than 30 years.
A INTERSECTION B = The set of employees whose are in S/W development department having age less than 30 years.

Difference:

The difference between two relations A and B( in that order) is the set of all tuples belonging to A and not to B.

Example:

A = The set of employees whose department is S/W Development
B = The set of employee whose age is less than 30 years.
A MINUS B = The set of employees whose department is S/W development and not having age less than 30 years.

Cartesian Product:

The Cartesian product of two relations A and B is the set of all tuples t such that t is the concatenation of a tuple a belonging to A and a tuple b belonging to B. The concatenation of a tuple a = (a1, ………., am) and tuple b=(bm+1 , ……., bm+n)- in that order- is the tuple t =(a1, ….., am, bm+1, ……..bm+n).

Example:

A = The set of employees whose department is S/W Development
B = The set of employee whose age is less than 30 years.
A TIMES B = is the set of all possible employee no/department ids pairs