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

try

SELECT id, m_name as "Mobile Name", cost as Price,(select avg(cost) from mobile) as Average),
cost-(select avg(cost) from mobile) as Difference FROM mobile
group by id,m_name,cost;

if your query is too expensive that way drop me a commend then I'll improve it.