MySQL SELECT query: i want show duplicated entries
If you really need it (I don't get why though), you can do 

SELECT code_CAT 
FROM categories a
INNER JOIN 
(
  select 14 as id_code
  UNION ALL
  select 14
  UNION ALL
  select 14
  UNION ALL
  select 14
)b ON (a.id_code = b.id_code)