How to calculate average of a column and then include it in a select query in oracle?

Question

My table is--

create table mobile
(
  id integer,
  m_name  varchar(20),
  cost integer
)

and the values are --

insert into         


        

Answer 1

Since you're using Oracle, you should be able to use AVG() as an analytic (window) function:

SELECT id, m_name AS "Mobile Name" cost AS Price, AVG(cost) OVER( ) AS Average
     , cost - AVG(cost) OVER ( ) AS Difference
  FROM mobile

No need for subqueries or GROUP BY.