Prerequisite: Create Table

    create table employees (
        id int primary key,
        name varchar(100) not null
    );
    insert into employees(id,name) values (1,'Naresh');
    insert into employees(id,name) values (2,'Siva');

Generate employee id automatically

     drop table employees;
     create table employees (
         id int primary key serial,
         name varchar(100) not null
    );

     insert into employees(name) values ('Naresh');
     insert into employees(name) values ('Siva');