SQL | DDL, DML, DCL Commands

Structured Query Language(SQL) is the database language which is used to perform certain operations on the existing database and also this language is used to create a database.

SQL uses certain commands like Create, Drop, Insert etc. to carry out the required tasks.

These some SQL commands are categories as discussed below:

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 database.

Examples of DDL commands:

CREATE

Create command is used to create the database or its objects (like table, index, function, views, store procedure and triggers).

Example:

CREATE TABLE Student(RollNumber varchar(20), StudentName varchar(255),  CollegeName varchar(255), Address varchar(255) );

DROP

Drop command is used to delete objects from the database.

Example: 

DROP TABLE Student;

ALTER

Alter command is used to alter the structure of the database.

Example:

ALTER TABLE Student ADD Email varchar(255);

TRUNCATE

Truncate command is used to remove all records from a table, including all spaces allocated for the records are removed.

Example:

TRUNCATE TABLE Student;

COMMENT

Comment command is used to add comments to the data dictionary. Use “–” or this “/* */” symbols for comment.

Example: 

--TRUNCATE TABLE Student;
or
/* TRUNCATE TABLE Student; */

RENAME

Rename command is used to rename an object existing in the database.

Example:

ALTER TABLE Student RENAME TO Vidhyarthi;

DML(Data Manipulation Language)

The SQL commands that deals with the manipulation of data present in database belong to DML or Data Manipulation Language and this includes most of the SQL statements.

Examples of DML commands:

SELECT

Select command is used to retrieve data from the a database.

Example:

SELECT * FROM Student;

INSERT

Insert command is used to insert data into a table.

Example:

INSERT INTO Student(RollNumber, StudentName varchar,  CollegeName, Address) VALUES ('123CS2019', 'Jayesh', 'ATC', 'Indore');

UPDATE

Update command is used to update existing data within a table.

Example:

UPDATE Student SET StudentName = 'Kumar', City= 'Burhanpur' 
WHERE RollNumber = '123CS2019';

DELETE

Delete command is used to delete records from a database table.

Example:

DELETE FROM Student WHERE RollNumber='123CS2019';

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

Grant command gives user’s, access privileges to database.

Example:

GRANT SELECT, INSERT ON Student TO 'Jayesh';

REVOKE

Revoke command withdraw user’s access privileges given by using the GRANT command.

Example:

REVOKE SELECT, INSERT ON Student TO 'Jayesh';