从当前月-11个月开始，到当前月为止，用一个sql语句计算出每个月的天数。

SELECT TO_CHAR(ADD_MONTHS(SYSDATE,-LEVEL+1),'YYYY-MM') MONTH , TO_CHAR(LAST_DAY(ADD_MONTHS(SYSDATE,-LEVEL+1)),'DD') DAY FROM DUAL CONNECT BY LEVEL <=12