Why does TO_CHAR not like me adding a fraction then specifying FF?

Question

Why does TO_CHAR not like me adding a fraction?
SQL> SELECT TO_CHAR(TO_TIMESTAMP('1/1/2012', 'DD/MM/YYYY') + .733409047, 'HH24:MI:SS') FROM Dual;
TO_CHAR(
17:36:07
SQL> SELECT TO_CHAR(TO_TIMESTAMP('1/1/2012', 'DD/MM/YYYY') + .733409047, 'HH24:MI:SS.FF') FROM Dual;
SELECT TO_CHAR(TO_TIMESTAMP('1/1/2012', 'DD/MM/YYYY') + .733409047, 'HH24:MI:SS.FF') FROM Dual
ERROR at line 1:
ORA-01821: date format not recognized
-- NUMTODSINTERVAL() saves the day.
SQL> SELECT TO_CHAR(TO_TIMESTAMP('1/1/2012', 'DD/MM/YYYY') + NUMTODSINTERVAL(.733409047, 'DAY'), 'HH24:MI:SS.FF') FROM Dual;
TO_CHAR(TO_TIMESTA
17:36:06.541660800

Answer 1

Hi,
Date arithmetic only works with DATEs.
If you want to do something similar with TIMESTAMPs, use NUMTODSINTERVAL:
SELECT  TO_CHAR ( TO_TIMESTAMP ('1/1/2012', 'DD/MM/YYYY') + NUMTODSINTERVAL (.733409047, 'DAY')
          , 'HH24:MI:SS.FF'
FROM      dual
;Here's exactly what's happending:
When you say "d + n", d is supposed to be either a NUMBER or a DATE. When you pass any other datatype, Oracle tries to convert d to either a NUMBER or a DATE. In this case, d was a TIMESTAMP; Oracle realized that it could convert that TIMESTAMP into a DATE, and did so. The 1st argument to TO_CHAR, therefore, was a DATE, but '.FF' only works with TIMESTAMPs.
There are a couple of things about how Oracle handles this that I find annoying, but I don't know of any better work-around.
Edited by: Frank Kulash on Feb 16, 2012 1:39 PM