The Data Definition Language (DDL) part of SQL permits database tables to be created or deleted. We can also define indexes (keys), specify links between tables, and impose constraints between database tables.
The most important DDL statements in SQL are:

• CREATE TABLE - creates a new database table
• ALTER TABLE - alters (changes) a database table
• DROP TABLE - deletes a database table

Syntax to create a database is

CREATE DATABASE dbname;

Eg: CREATE DATABASE GJUniv;

The SQL statement to create a table has the basic form:
CREATE TABLE name( col1 datatype, col2 datatype, …);

Eg:
CREATE TABLE User (FirstName TEXT, LastName TEXT, UserID TEXT, Dept TEXT, EmpNo INTEGER, PCType TEXT );

Once a table is created it's structure is not necessarily fixed in stone. In time requirements change and the structure of the database is likely to evolve to match your wishes. SQL can be used to change the structure of a table, so, for example, if we need to add a new field to our User table to tell us if the user has Internet access, then we can execute an SQL ALTER TABLE command as shown below:

ALTER TABLE User ADD COLUMN Internet BOOLEAN;

To delete a column the ADD keyword is replaced with DROP, so to delete the field we have just added the SQL is:
ALTER TABLE User DROP COLUMN Internet;

If you have already executed the original CREATE TABLE command your database will already contain a table called User, so let's get rid of that using the DROP command:

DROP TABLE User;

And now we'll recreate the User table we'll use throughout the rest of this tutorial:

CREATE TABLE User (FirstName VARCHAR (20), LastName VARCHAR (20),
UserID VARCHAR(12) UNIQUE, Dept VARCHAR(20), EmpNo INTEGER UNIQUE, PCType VARCHAR(20);