What is a query language in DBMS?

Query is a question or requesting information. Query language is a language which is used to retrieve information from a database.

Query language is divided into two types as follows −

Procedural language
Non-procedural language

Procedural language

Information is retrieved from the database by specifying the sequence of operations to be performed.

For Example: Relational algebra

Structure Query language (SQL) is based on relational algebra.

Relational algebra consists of a set of operations that take one or two relations as an input and produces a new relation as output.

The different types of relational algebra operations are −

Select operation
Project operation
Rename operation
Union operation
Intersection operation
Difference operation
Cartesian product operation
Join operation
Division operation.

Select, project, rename comes under unary operation (operate on one table). Union, intersection, difference, cartesian, join, division comes under binary operation (operate on two tables).

Non-Procedural language

Information is retrieved from the database without specifying the sequence of operation to be performed. Users only specify what information is to be retrieved.

For Example: Relational Calculus

Query by Example (QBE) is based on Relational calculus

Relational calculus is a non-procedural query language in which information is retrieved from the database without specifying sequence of operation to be performed.

Relational calculus is of two types which are as follows −