show parameter RESULT_CACHE_MODE

SELECT dbms_result_cache.status() FROM dual;

CREATE TABLE test_table
(n_number int, 
 n_size varchar2(5));

INSERT INTO test_table VALUES (85,'Small');

INSERT INTO test_table VALUES (92,'Small');

COMMIT;

set autotrace on explain statistics

SELECT n_size, avg(n_number)
  FROM test_table
 GROUP BY n_size;

SELECT /*+ RESULT_CACHE */ n_size, avg(n_number)
  FROM test_table
 GROUP BY n_size;

SELECT /*+ RESULT_CACHE */ n_size, avg(n_number)
  FROM test_table
 GROUP BY n_size;

-- Clean Up

DROP TABLE test_table PURGE;