Database Languages Database Management System

Database Languages Database Management System

DATA BASE LANGUAGES

Irrespective of the type of database, every database supports following three types of language/ Commands:

(1) DDL (Data Definition Language)

(2) DML (Data Manipulation Language)

(3) DCL (Data Control Language)

Data Definition Language (DDL)

DDL is used to define the conceptual schema of the database. Its is a set of SOL command used to create, modify and delete database structures but not data. These commands are normally not used by a general user, who should be accessing the database via an application. They are generally used by the DBA, a database designer or application developer. These statements cannot be Roll backed.

The few SOL commands available in oracle for DDL are:

(a) Create table

(b) Alter Table

(c) Drop Table

DDL also updates a special set of table called the data dictionary or data directory.

A data dictionary contains metadata, i.e., data about data. The schema of table is an example of metadata. A database System consults the data dictionary before reading or modifying actual data.

 

Data Manipulation Language (DML)

A DML is a language that enables user to access or manipulate data stored in the database. The DML. provides Commands to select, retrieve, delete, modify data. These command are given in the form of query.

Though DML, we can:

  1. Insert the new data in the database : For example, if a student joins the institute then we have to ins the information in the student database. The SQL Command in oracle for inserting data in the table is “ins into <tablename> values <values”

DBMS Architecture

  1. Modify the data stored in the database : For example, in student database, if a student changes his address than we have to modify the record in the table. The SOL command in oracle for modifying data is “update <tablename> set <field>=<values”

 

  1. Deletion of the Data : For example, if a student leaves the institute then we have to delete the record from the database. The SOL command in oracle for deleting data is “delete from <tablename> where <condition>”

 

 

  1. Retrieve the information : For example, if we want to display the date of birth of all students than we have to write the query statement for the information. The SOL command in oracle for retrieving is “select *from <tablename> where <condition>”

 

Data Control Language (DCL)

 

Through DCL we can control access to data and to the database. Sometimes DCL statements are grouped with DML statements.

Through DCL, we can :

  1. Commit : Permanently Save the data in physical database.
  2. Roll back : Restore database to original state since the last commit statement
  3. Grant : Grant various types of permissions to the users.