oracle:

SELECT ename, hiredate,add_months(hiredate, 1) "1", add_months(hiredate, 2) "2" FROM emp where rownum < 7

MySQL

SELECT ename, hiredate, DATE_ADD(hiredate, INTERVAL 31 DAY)"d-add31", adddate(hiredate, INTERVAL 60 DAY)"add-d62" from emp limit 6

postgresql

SELECT ename, hiredate, DATE(hiredate + 31 )"d-add31", date(hiredate + 60 )"add-d62" from emp limit 6

 
Oracle
POSTGRESQL

MySQL