确定指定年份季度的开始日期和结束日期

SELECT sn AS 季度,
       (sn - 1) * 3 + 1 AS 开始月份,
       ADD_MONTHS(TRUNC(TO_DATE(年, 'yyyy'), 'yy'), (sn - 1) * 3) AS 开始日期,
       ADD_MONTHS(TRUNC(TO_DATE(年, 'yyyy'), 'yy'), sn * 3) - 1 AS 结束日期
  FROM (SELECT '2015' AS 年, LEVEL AS sn FROM DUAL CONNECT BY LEVEL <= 4);