Oracle 11g Release 2

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CREATE TABLE test (date_last_run DATE, value NUMBER, frequence VARCHAR2(10) );
INSERT INTO test ( date_last_run, value, frequence )
  SELECT sysdate,           -1, 'MONTH' FROM DUAL UNION ALL
  SELECT DATE '2019-03-31', -1, 'MONTH' FROM DUAL UNION ALL
  SELECT DATE '2020-02-29', -1, 'YEAR'  FROM DUAL
3 rows affected

SELECT t.*,
       CASE frequence
       WHEN 'MONTH' THEN add_months( date_last_run, value )
       WHEN 'YEAR'  THEN add_months( date_last_run, 12 * value )
       END AS updated_date
FROM   test t


DATE_LAST_RUN
VALUE
FREQUENCE
UPDATED_DATE


18-SEP-19
-1
MONTH
18-AUG-19

31-MAR-19
-1
MONTH
28-FEB-19

29-FEB-20
-1
YEAR
28-FEB-19

DATE_LAST_RUN	VALUE	FREQUENCE	UPDATED_DATE
18-SEP-19	-1	MONTH	18-AUG-19
31-MAR-19	-1	MONTH	28-FEB-19
29-FEB-20	-1	YEAR	28-FEB-19