取制定月份的天数

Question

如何取得指定月份一共多少天，用SQL语句实现

Answer 1

select to_char(add_months(to_date(&year || '-' || &month || '-' || '01',
                                  'yyyy-mm-dd'),
                          1) - 1,
               'dd')
  from dual

Answer 2

select substr(to_char(last_day(to_date('2008-9','yyyy-mm')),'yyyy-mm-dd'),9) days  from dual;
想要哪个月就把2008-9改成那个月份

Answer 3

或者
select to_char(last_day(to_date(&year || '-' || &month || '-' || 01,
                                'yyyy-mm-dd')),
               'dd')
  from dual