Difference Between Timestamps in Milliseconds in Oracle

Question

I have table test1 and have one column DOJ with timestamp datatype having few records as shown below. Here i need the difference im milliseconds between doj and systimestamp.

SELECT DOJ FROM TEST1; 
DOJ 
---------------------------- 
21-MAR-14 09.25.34.514526000 
21-MAR-14 09.25.34.520345000 
22-MAR-14 09.25.34.523144000 
22-MAR-14 09.25.34.527770000 
23-MAR-14 09.25.34.532482000 
23-MAR-14 09.25.34.535603000 
24-MAR-14 09.25.34.538556000 
24-MAR-14 09.25.34.541729000 

SELECT SYSTIMESTAMP FROM DUAL; 
SYSTIMESTAMP 
-------------- 
24-MAR-14 09.48.10.251556000 +00:00 

Can some one please help me with this.

Answer 1

Expanding René's answer a bit, if you want the total milliseconds then you need to extract and combine all of the elements from the interval that's produced by subtracting one timestamp from another:

select doj, systimestamp - doj,
  trunc(1000 * (extract(second from systimestamp - doj)
    + 60 * (extract(minute from systimestamp - doj)
      + 60 * (extract(hour from systimestamp - doj)
        + 24 * (extract(day from systimestamp - doj) ))))) as milliseconds
from test1;

DOJ                          SYSTIMESTAMP-DOJ     MILLISECONDS
---------------------------- ---------------- ----------------
21-MAR-14 09.25.34.514526000 3 2:9:8.785713          266948785 
21-MAR-14 09.25.34.520345000 3 2:9:8.779894          266948779 
22-MAR-14 09.25.34.523144000 2 2:9:8.777095          180548777 
22-MAR-14 09.25.34.527770000 2 2:9:8.772469          180548772 
23-MAR-14 09.25.34.532482000 1 2:9:8.767757           94148767 
23-MAR-14 09.25.34.535603000 1 2:9:8.764636           94148764 
24-MAR-14 09.25.34.538556000 0 2:9:8.761683            7748761 
24-MAR-14 09.25.34.541729000 0 2:9:8.75851             7748758 

SQL Fiddle, including the Unix epoch date for comparison, though you'd need to adjust that for your server time zone.

Answer 2

select
  extract(second from systimestamp - doj) * 1000
from
  test1;