Page 6 - Relational Databases

SQL
Structured Query Language or SQL is the most widely implemented and used language for
relational database management systems.
SQL is a unified, non-procedural language used for creating, accessing, handling and
managing data in a relational database.

Types of SQL statements
The SQL statements are categorized into different categories based upon the purpose. They
are:
i. Data Definition Language (DDL)
ii. Data Manipulation Language (DML)
iii. Data Query Language (DQL)
iv. Data Control Language (DCL)
v. Transaction Control Language (TCL)

DDL(Data Definition Language) : DDL or Data Definition Language actually consists of the
SQL commands that can be used to define the database schema. It simply deals with
descriptions of the database schema and is used to create and modify the structure of
database objects in the database.
Examples of DDL commands:
CREATE, DROP, ALTER, TRUNCATE, CPOMMENT, RENAME

DML(Data Manipulation Language) : The SQL commands that deals with the manipulation
of data present in the database belong to DML or Data Manipulation Language and this
includes most of the SQL statements.
Examples of DML: INSERT, UPDATE, DELETE

DQL (Data Query Language) : DML statements are used for performing queries on the data
within schema objects. The purpose of DQL Command is to get some schema relation based
on the query passed to it.
Example of DQL: SELECT

DCL(Data Control Language) : DCL includes commands such as GRANT and REVOKE which
mainly deals with the rights, permissions and other controls of the database system.
Examples of DCL commands: GRANT, REVOKE

TCL(transaction Control Language) : TCL commands deals with the transaction within the
database.
Examples of TCL commands: COMMIT, ROLLBACK, SAVEPOINT etc