ORA-01843 "Invalid month" and ORA-01861 "Literal does not match format string"

Question

SQL> select to_timestamp('2010-12-14:09:56:53') - to_timestamp('2010-12-14:09:56:46') from dua
l;
select to_timestamp('2010-12-14:09:56:53') - to_timestamp('2010-12-14:09:56:46') from dual
                    *
ERROR at line 1:
ORA-01843: not a valid month


SQL> select to_date('2010-12-14:09:56:53') - to_date('2010-12-14:09:56:46') from dual;
select to_date('2010-12-14:09:56:53') - to_date('2010-12-14:09:56:46') from dual
               *
ERROR at line 1:
ORA-01861: literal does not match format string

What is the right way to do

2010-12-14:09:56:53
minus
2010-12-14:09:56:46

in Oracle SQL?

Answer 1

You must specify the format in which the timestamp string is located, in TO_DATEand TO_TIMESTAMP:

select 
    to_date('2010-12-14:09:56:53', 'YYYY-MM-DD:HH24:MI:SS') - 
    to_date('2010-12-14:09:56:46', 'YYYY-MM-DD:HH24:MI:SS') 
from dual;

The result will be in days, which you can multiply by 86,400 to get seconds:

TO_DATE('2010-12-14:09:56:53','YYYY-MM-DD:HH24:MI:SS')-TO_DATE('2010-12-14:09:56
--------------------------------------------------------------------------------
.000081019

---

Usage TO_TIMESTAMP:

select 
    to_timestamp('2010-12-14:09:56:53', 'YYYY-MM-DD:HH24:MI:SS') - 
    to_timestamp('2010-12-14:09:56:46', 'YYYY-MM-DD:HH24:MI:SS') 
from dual;

The result will be in the format TIMESTAMP:

TO_TIMESTAMP('2010-12-14:09:56:53','YYYY-MM-DD:HH24:MI:SS')-TO_TIMESTAMP('2
---------------------------------------------------------------------------
+000000000 00:00:07.000000000

Answer 2

Use to_timesatmp

select TO_TIMESTAMP('2010-12-14:09:56:53',  'YYYY-MM-DD:HH24:MI:SS.FF') 
 - TO_TIMESTAMP('2010-12-14:09:56:46',  'YYYY-MM-DD:HH24:MI:SS.FF') 

from dual