Relational Query Languages

What is Relational Query Languages?

Relational database systems come with query languages that help users to query database instances. A query language allows users to request information from the database, with SQL (Structured Query Language) being a common example. Queries can be seen as "retrieval programs."

Types of Query Languages

There are two main types of query languages:

1. Procedural Query Language

⇒ Users instruct the system to perform a series of operations to get the desired results.

⇒ Users specify what data to retrieve and how to retrieve it.

2. Non-Procedural (Declarative) Query Language

⇒ Users specify the desired result without detailing the steps to achieve it.

⇒ Users tell what data to retrieve but not how to retrieve it.

Pure Query Languages

There are two "pure" query languages, which are mathematical in nature:

1.Relational Algebra

A procedural query language.

⇒ It is operational and useful for representing execution plans.

⇒ Users specify what data is required and how to get that data.

2.Relational Calculus

A non-procedural query language.

⇒ Includes Tuple Relational Calculus and Domain Relational Calculus.

⇒ Users specify what data they want without specifying how to get it.