Introduction to database management systems

SQL is a programming language for Relational Databases. SQL consists both data definition and data manipulation languages.

Data Definition Language

Data Definition Language (DDL) is a standard for commands that define different structures in a database.

• CREATE - to create objects in database like databases, tables and views
  
  Create database db_1;
Create table dtable;
Create view dview;

•  ALTER - alter structure of database
  
  Alter table dtable add subject varchar;

•  DROP - delete objects from database like view,table
  
  Drop database db_1;
Drop table dtable;
Drop view dview;


• TRUNCATE - remove all records from a table, including all spaces allocated. 
  
  TRUNCATE TABLE dtable;

 (DML) statements are used for managing data within schema objects.Data Manipulation Language

• SELECT - retrieve data from a database 
  
  SELECT * from dtable; // query returns all data stored in dtable

• INSERT - insert data into a table 

• UPDATE - updates existing data within a table 

• DELETE - deletes all records from a table, space for records remain