orderingEmails

My solution:

CREATE PROCEDURE orderingEmails() 
BEGIN 
  SELECT id, 
         email_title, 
         IF(size >= POWER(2, 20), CONCAT(FLOOR(size / POWER(2, 20)), " Mb"), 
         CONCAT(FLOOR(size / POWER(2, 10)), " Kb")) AS short_size 
  FROM   emails 
  ORDER  BY size DESC; 
END