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