Cannot convert to date, getting “ORA-01855: AM/A.M. or PM/P.M. required” error message

Question

the following code gives me this error message - "ORA-01855: AM/AM or PM/PM required"

SELECT TO_DATE
    ('2/2/2021 8:08:58 PM','MM/DD/YYYY HH:MI:SS AM') "NOW"
     FROM DUAL;

If I try to convert to char instead, I get "ORA-01722: invalid number".

     SELECT TO_CHAR('2/2/2021 8:08:58 PM', 'MM/DD/YYYY HH:MI:SS AM') "NOW"
     FROM DUAL;

I don't have much experience with oracle database and have been struggling with it for a while. Not sure what I'm doing wrong. Thanks for any help!

Answer 1

It looks like you probably have NLS_DATE_LANGUAGE set to something other than English; but not NLS_LANGUAGE as that would affect the error message too:

alter session set nls_language = 'CZECH';

SELECT TO_DATE
    ('2/2/2021 8:08:58 PM','MM/DD/YYYY HH:MI:SS AM') "NOW"
     FROM DUAL;

ORA-01855: požaduje se AM/A.M. nebo PM/P.M.

With just the date language changed:

alter session set nls_language = 'ENGLISH';
alter session set nls_date_language = 'CZECH';

SELECT TO_DATE
    ('2/2/2021 8:08:58 PM','MM/DD/YYYY HH:MI:SS AM') "NOW"
     FROM DUAL;

ORA-01855: AM/A.M. or PM/P.M. required

You can either change the session setting to English, or change the string to have the language-appropriate AM/PM indicator value:

alter session set nls_date_language = 'CZECH';

SELECT TO_DATE
    ('2/2/2021 8:08:58 ODPOLEDNE','MM/DD/YYYY HH:MI:SS AM') "NOW"
     FROM DUAL;

NOW
---------
02-ÚNO-21

Or probably most practically and simply, override the session setting in the query:

alter session set nls_date_language = 'CZECH';

SELECT TO_DATE
    ('2/2/2021 8:08:58 PM','MM/DD/YYYY HH:MI:SS AM','NLS_DATE_LANGUAGE=ENGLISH') "NOW"
     FROM DUAL;

NOW
---------
02-ÚNO-21

db<>fiddle

Answer 2

You should use TO_CHAR to convert from date to char, not from char:

SELECT TO_CHAR(TO_DATE('2/2/2021 8:08:58 PM', 'MM/DD/YYYY HH:MI:SS AM'),
               'MM/DD/YYYY HH:MI:SS AM') "NOW"
  FROM DUAL;