Monday, July 9, 2018

Different Types of SQL Commands



SQL commands can be classified into following types:

·         DDL – Data Definition Language
·         DML – Data Manipulation Language
·         DQL – Data Query Language
·         DCL – Data Control Language
·         TCL – Transaction Control Language


1.    DDL (Data Definition Language): These commands used to work on the Structure or Definition of the data. Following are DDL commands:

a)   CREATE             -        used to create database and its objects.
b)   ALTER               -        used to alter the database structure
c)    DROP                -        used to drop the database objects.
d)   TRUNCATE       -        used to remove all data records along with resetting the identity i.e. removing the allocated space also.
e)   COMMENT          -        used to add comments
f)     RENAME            -        used to rename existing database objects.

 2.    DML (Data Manipulation Language): These commands used to work on the data itself. It helps in manipulating the data within the database tables. Following are DML commands:

a)   INSERT              -        used to insert data in database table
b)   UPDATE             -        used to update data in database table
c)    DELETE             -        used to delete data records.

 3.    DQL (Data Query Language): Deals with the data but only to retrieve the data. Following is DQL command:

a)   SELECT             -        used to query/select and retrieve the data records

 4.    DCL (Data Control Language): These commands control the data and mainly deals with providing/ revoking the rights, permissions and other controls of the database system. Following are the DCL commands:

a)   GRANT              -        assign privileges to user to use database.
b)   REVOKE             -        withdraw privileges to user to use database.
c)    DENY           -       deny user privileges on database such as using UPDATE statement on database tables.

 5.    TCL (Transaction Control Language): These commands deal with the transaction management in SQL server. Following are the TCL commands:

a)   COMMIT            -        commit a transaction.
b)   ROLEBACK         -       rollback uncommitted transactions in case of any error.
c)    SAVEPOINT       -        sets a save-point within a transaction.
d)   SET TRANSACTION     -        specify characteristics for the transaction.


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