上季度所有月份：

SELECT TO_CHAR(ADD_MONTHS(ADD_MONTHS(TRUNC(SYSDATE,'YYYY'),A * 3),-ROWNUM),'YYYYMM')  LAST_Q  
    FROM (SELECT TO_CHAR(SYSDATE,'Q')-1 A FROM DUAL)  
    CONNECT BY ROWNUM <= 3  
    ORDER BY 1;

本季度所有月份：

SELECT TO_CHAR(ADD_MONTHS(ADD_MONTHS(TRUNC(SYSDATE,'Q') A FROM DUAL)  
    CONNECT BY ROWNUM <= 3  
    ORDER BY 1;