Convert milliseconds to Timestamp

Question

I know that to convert a Unix timestamp in milliseconds to an SQL timestamp I can use

SELECT TO_DATE('1970-01-01','YYYY-MM-DD HH24:MI:SS') + 
       (:timestamp / (1000*60*60*24)) FROM DUAL;

But I need a Timestamp, so I tried with

SELECT TO_TIMESTAMP('1970-01-01 00:00:00','YYYY-MM-DD HH24:MI:SSFF3') + 
       (:timestamp) from DUAL

Which gives me the error:

Error: ORA-01841: (full) year must be between -4713 and +9999, and not be 0

It seems that adding 1 to the timestamp always converts it to a day.

How can I do the same to get a real timestamp?

Answer 1

You will get a timestamp if you add an interval to a timestamp (see date/interval arithmetics).

As Benoit noticed, you can't specify an interval with seconds when there are more than about 2.1e9 of them:

SQL> SELECT numtodsinterval(2.2e9, 'SECOND'),
  2         numtodsinterval(2.3e9, 'SECOND')
  3    FROM dual;

NUMTODSINTERVAL(2.2E9,'SECOND'  NUMTODSINTERVAL(2.3E9,'SECOND'
------------------------------- -------------------------------
+000024855 03:14:07.147483647   +000024855 03:14:07.147483647

This is why you should use minutes which do not lose precision. For example, assuming :TS is the unix timestamp (i.e. a number):

SQL> variable ts number;
SQL> -- determining unix timestamp with nanosecond precision
SQL> BEGIN
  2     :ts := (to_date('2099-01-01 01:02:03', 'yyyy-mm-dd hh24:mi:ss')
  3              - date '1970-01-01') * 1000*60*60*24
  4            + 123.456789;
  5  END;
  6  /

ts
---------
4070912523123,456789

SQL> select timestamp '1970-01-01 00:00:00'
  2         + numtodsinterval((:ts)/1000/60, 'MINUTE')
  3    from dual;

TIMESTAMP'1970-01-0100:00:00'+NUMTODSINTERVAL((:TS)/1000/60,'MINUTE')
---------------------------------------------------------------------------
2099-01-01 01:02:03.123456789