SQL stands for Structured Query Language, SQL is not a database system, it is a Query language. SQL is used for storing, manipulating and retrieving data in databases.

There are following five types of SQL commands as DDL, DML, DCL, TCL, and DQL.

1- DDL – Data Definition Language
2- DQl – Data Query Language
3- DML – Data Manipulation Language
4- DCL – Data Control Language
5- TQL – Transaction Control Language

_{1- DDL (Data Definition Language ):: This SQL commands deals with descriptions of the database schema and is used to create and modify the structure of database objects in the database. It is a set of SQL commands used to create, modify, and delete database structures but not data.}

_{The following below list of DDL commands}

_{CREATE – Used to create the database or its objects (like table, index, function, views, store procedure, and triggers).
DROP – Used to delete objects from the database.
ALTER – Used to alter the structure of the database.
TRUNCATE – Used to remove all records from a table, including all spaces allocated for the records are removed.}

_{2- DML (Data Manipulation Language) :: This SQL commands , deals with the manipulation of data present in the database belonging to DML (Data Manipulation Language) and this includes most of the SQL statements.} 

_{The following below list of DML commands}

_{INSERT – Used to insert data into a table.
UPDATE – Used to update existing data within a table.
DELETE – Used to delete records from a database table.
LOCK – Used to table control concurrency.}

_{3- DCL (Data Control Language) :: This SQL commands deals as GRANT and REVOKE which mainly deal with the rights, permissions, and other controls of the database system.}

_{GRANT – This command allows users access privileges to the database.
REVOKE – This command withdraws the user’s access privileges given by using the GRANT command}

_{4- TCL (Transaction control language) :: This SQL commands deals with the transaction within the database}

_{The following below list of TCL commands}

_{COMMIT – Used to Commit a Transaction.
ROLLBACK – Used to Rollback a transaction in case of any error occurs.
SAVEPOINT – Used to Set a savepoint within a transaction.}

_{5- TQL (Transaction Control Language):: Used to fetch the data from the database, It uses only one command}

_{The following below one TQL command}

_{Select – Used to select data from database table.}

Database View ::

“Database View is a virtual table based on the result-set of an SQL statement. A view contains rows and columns, like a real table.”

“Database views are created using the CREATE VIEW statement. Views can be created from a single table, multiple tables or another view.”

CREATE VIEW Syntax:: −

CREATE VIEW view_name AS
SELECT column1, column2…..
FROM table_name
WHERE [condition];

Database View also allow to include multiple tables in your SELECT statement

Example
Consider the CUSTOMERS_INFO table having the following records −

ID	NAME	AGE	ADDRESS	SALARY
1	John	32	New York	2000.00 $
2	Mary	25	Paris	1500.00 $
3	Smith	23	Singapore	2000.00 $
4	Steve	25	London	6500.00 $
5	Rindy	27	Sydney	8500.00 $

Following below example to create a View from the CUSTOMERS_INFO table. This view would be used to have customer name and age from the CUSTOMERS_INFO table.

SQL > CREATE VIEW CUSTOMERS_VIEW AS
SELECT name, age
FROM CUSTOMERS;

Now, you can query CUSTOMERS_VIEW in a similar way as you query an actual table.

Following is an example for the same.

SQL > SELECT * FROM CUSTOMERS_VIEW;

Result as below

Name	Age
John	32
Mary	25
Smith	23
Steve	25
Rindy	27