How can i add one month to a date variable ?

Question

Unlike the week which always 7 days, month may change from 28 to
31, so how can i add one month to a date variable ? Thanks in
advance.

Answer 1

Adding 365 won't always work because of leap years.
You could use the following SQL statement:
SELECT
     TO_DATE(
          TO_CHAR(TO_DATE(SYSDATE), 'DD-MON-') ||
            (TO_CHAR(TO_DATE(SYSDATE), 'YYYY') + 1)) NEXT_YEAR
FROM
     dual
NEXT_YEAR
08-JAN-03Or you could create your own function. You would use this
exactly like add_months:
CREATE OR REPLACE FUNCTION add_years
     (v_date DATE, num_years NUMBER)
RETURN DATE AS
     v_year DATE;
BEGIN
     v_year := TO_DATE(
               TO_CHAR(TO_DATE(SYSDATE), 'DD-MON-') ||
                     (TO_CHAR(TO_DATE(SYSDATE), 'YYYY')
                                         + num_years));
     RETURN v_year;
END;     
SELECT
     add_years(SYSDATE, 1) new_year
FROM
     dual
NEW_YEAR 
08-JAN-03
SELECT
     add_years(SYSDATE, -1) new_year
FROM
     dual
NEW_YEAR 
08-JAN-01