หาความต่าง วัน เวลา ,วันที่เริ่มต้น-วันที่สิ้นสุด ORACLE pl/sql

function CF_DIF_DATEFormula return VARCHAR is
    days number;
    hr   number;
  mm   number;
  vTmp_ret      varchar2(100);
  temp varchar2(100);
begin
  days     := trunc(:startup_date) - trunc(:break_date);
    hr        := trunc((:startup_time - :break_time)/3600) ;
    mm    := trunc( mod((:startup_time - :break_time) , 3600 ) / 60 ) ;
  temp  := '  ';
  
    IF trunc(:startup_date) = trunc(:break_date) THEN
        vTmp_ret     := (replace(to_char(hr,'99')||' ชม   '||to_char(mm,'99')||' นาที',' ',''));
  
    ELSIF trunc(:startup_date) <> trunc(:break_date) THEN
          IF :startup_time = :break_time THEN
              vTmp_ret  := (replace(to_char(days,'99,999')||' วัน  ',' ',''));
        
          ELSIF :startup_time <> :break_time THEN
              IF :break_time < :startup_time THEN
                  days     := days;
                    hr        := hr ;
                    mm    := mm ;
              ELSIF :break_time > :startup_time THEN
                  days             := days -1;
                 hr                := trunc((86400-(:break_time - :startup_time))/3600) ;
                 mm        := trunc( mod((:break_time - :startup_time) , 3600 ) / 60 ) ;
              END IF;
          ----------------------------------------------------------------------------------------------------------------
          IF days = 0 THEN
              vTmp_ret  := (replace(to_char(hr,'99')||' ชม   '||to_char(mm,'99')||' นาที',' ',''));
          ELSE
              vTmp_ret  := (replace(to_char(days,'99,999')||' วัน '||'   '||to_char(hr,'99')||' ชม   '||to_char(mm,'99')||' นาที ',' ',''));
          END IF;
            ----------------------------------------------------------------------------------------------------------------
  
          END IF;
        
    END IF;
   
     return(vTmp_ret);
end;