Query with CAST and IN operator

Hi Team,

Query with CAST operator taking more time where as IN is taking lesstime.

Database : 11.2 OS:Sun Solaris 10

We are asked to use CAST in the query, can you please share details which operator is good in this case.

Query with CAST -

SELECT DISTINCT A.ID ID, a.id_object_to id_object_to,
  DECODE( ATO.id_association,NULL,a.id_object_what,ATO.id_object_what) id_object_what_override,
  a.id_object_what id_object_what,
  ATO.id_association id_association
FROM ASSOCIATION A,
  ASSOCIATION_TYPE AT,
  OBJECT_TYPE OT,
  (SELECT id_object_what,id_association
  FROM ASSOCIATION_TEMP_OVERRIDE