Prerequisite: Create Table

   create table employees(id NUMBER,name VARCHAR2(20));
   insert into employees(id,name) values (1,'Naresh');
   select * from employees;

Task 1: Alter Table - add column

    alter table employees add  dob date;
    alter table employees add  created_date timestamp;

    desc employees;

Task 2: Alter Table - Drop column

    alter table employees drop column created_date;

    desc employees;

Task 3: Alter table - Modify column

    alter table employees modify column name varchar(100);

    desc employees;