oracle计算两个时间的差值（XX天XX时XX分XX秒）

在工作中需要计算两个时间的差值，结束时间 - 开始时间，又不想在js里写function，也不想在java里去计算，干脆就在数据库做了一个函数来计算两个时间的差值。格式为XX天XX时XX分XX秒；

上代码：

CREATE OR REPLACE FUNCTION F_GET_DIFF_TIME(START_TIME IN DATE,
                                           END_TIME   IN DATE)
  RETURN VARCHAR2 IS
  DIFF_TIME VARCHAR2(50);
BEGIN
  SELECT TDAY || '天' || THOUR || '时' || TMINUTE || '分' || ROUND((TT - TMINUTE) * 60) || '秒' INTO DIFF_TIME
    FROM (SELECT TDAY,
                 THOUR,
                 TRUNC((TT - THOUR) * 60) TMINUTE,
                 (TT - THOUR) * 60 TT
            FROM (SELECT TDAY,
                         TRUNC((TT - TDAY) * 24) THOUR,
                         (TT - TDAY) * 24 TT
                    FROM (SELECT TO_NUMBER(END_TIME - START_TIME) AS TT,
                                 TRUNC(TO_NUMBER(END_TIME - START_TIME)) AS TDAY
                            FROM (SELECT START_TIME, END_TIME FROM dual))));

  RETURN DIFF_TIME;
END;

输出的格式为上图；