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;