introduction to relational algebra - Wikitechy

What is Relational Algebra in DBMS ?

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A procedural query language which is used widely is known as Relational Algebra.
Instances of relation are given as input data and we get output as occurrences of relations
Relational algebra uses various operations to perform this input and output action.
In a relation sql relational query operations are performed recursively.
Output for the above operations is a new relation, which is formed from one or more input relations.

Types of Relational Operation

Select Operation

Tuples that satisfy a given predicate is selected by select operation.
It is denoted by sigma(σ).
Notation: σ p(r)
- Where (σ) is used for selection prediction.
- R is used for relation,
- p is used as a propositional logic formula which may use connectors like: AND OR and NOT.

Project Operation

List of attributes that wish to appear in the result is shown in project operation.
Remaining attributes are eleminated from the table.
It is denoted by ∏.

Union Operation

In union there are two tuples, R and S.
The union operation that contains all the tuples are either in R or S or both in R & S.
It eliminates the duplicate tuples. It is denoted by ∪.

Notation: R ∪ S

Following condition should be held by Union operation.
R and S must have the attribute of the same number.
Duplicate tuples are eliminated automatically.

Set Intersection

Let us consider there are two tuples R and S. The set intersection operation contains all tuples that are in both R & S.
It is denoted by intersection ∩.
Notation: R ∩ S

Cartesian product

The Cartesian product is used to combine each row in one table with each row in the other table. It is also known as a Cross product.
It is denoted by X.
Notation: E X D

Rename Operation

The rename operation is used to rename the output relation. It is denoted by rho(ρ).