要顯示每月的每一天的數據，哪怕那天沒有數據也要顯示出來日期

select to_char(to_date('201908','yyyymm')+(rownum-1),'dd') DAY_ID
from dual  
connect by rownum<=to_number(to_char(last_day(to_date('201908','yyyymm')),'dd'))