6. Relational Algebra

Relational Algebra

Relational Algebra is a procedural query language used in relational databases.
It uses a set of mathematical operations to manipulate relations (tables) and produce new relations as output.

Here we cover four basic operations:

 

1. Union ( ∪ )

Definition:

Combines tuples (rows) from two relations and removes duplicates.

Requirements:

·       Both relations must be union-compatible (same number of attributes, same data types).

Example:

A ∪ B

Gives all tuples present in either A or B.

 

2. Intersection ( ∩ )

Definition:

Returns only those tuples that are present in both relations.

Example:

A ∩ B

Gives common tuples of A and B.

 

3. Set Difference ( − )

Definition:

Returns tuples that are in the first relation but not in the second.

Example:

A − B

Gives tuples that exist in A but not in B.

 

4. Cartesian Product ( × )

Definition:

Combines every tuple of the first relation with every tuple of the second relation.

Example:

A × B

Produces a large table with all possible combinations.

·       .

Used for:

Basis of JOIN operations in databases