Time difference Function

create or replace function tsdiff(ts1 in timestamp, ts2 in timestamp, units in varchar2)
/* units - l=millisecond s=second, m=minute, h=hour, d=day */
return number
is
  diff interval day(9) to second(9) := ts1 - ts2;
begin
  return (
             extract(day from diff)*24*60*60
           + extract(hour from diff)*60*60
           + extract(minute from diff)*60
           + extract(second from diff)
         ) / case (lower(units))
            when 'l' then 1/1000
            when 's' then 1
            when 'm' then 60
            when 'h' then 60*60
            when 'd' then 24*60*60