Oracle SQL to_date function not working on concatenated strings - sql

Question

I've been looking for a reason that this isn't working for quite some time. I'm concatenating two fields and attempting to run some date comparisons but it throws the error ORA-01843: not a valid month. I'm not sure what I'm doing wrong here.
Here's my code:
SELECT
sm.semester_date || cp.start_year AS effective
FROM
database.table cp,
database.table2 sm
WHERE cp.semesters_id = sm.semesters_id
AND to_date(sm.semester_date || cp.start_year, 'MM/DD/YYYY') >= to_date('06/01/2011', 'MM/DD/YYYY')
It runs fine as long as I don't add that AND statement at the end. But I need to filter the dataset.
When you run it without the filter it returns 08/15/2010 etc.
I forgot to add the mask originally when I posted this, I've corrected that. However, it still returns this error ORA-01840: input value not long enough for date format.
EDIT SOLUTION FOUND:
Firstly, thanks to everyone for helping me with this, you guys are great. Secondly, my error was being caused by a course without a start year. Very frustrating since that shouldn't be able to happen. Because the concatenated item had no year on it, it was throwing the error. I only found this because you guys helped me fix my code up. Thank you.

Answer 1

Try adding a separator between date and year:
SELECT
sm.semester_date || '/' || cp.start_year AS effective
FROM
database.table cp,
database.table2 sm
WHERE cp.semesters_id = sm.semesters_id
AND to_date(sm.semester_date || '/' || cp.start_year) >= to_date('06/01/2011', 'MM/DD/YYYY')
If you run the query without the filter, what does it return?

Answer 2

My guess is that your default date format does not match the format of the string that you are passing to TO_DATE. Add a format string as a second parameter to the call (as you've done for the second call) to specify what the format of the concatenated string is.

Answer 3

Is the SEMESTER_DATE column a VARCHAR2? And if so, is it a string in the format 'MM/DD/'? Or just 'MM/DD'?
As lweller points out, the first TO_DATE is also missing the format mask which would be a problem if your session's NLS_DATE_FORMAT is anything other than 'MM/DD/YYYY'.
Assuming SEMESTER_DATE is a VARCHAR2 in the format 'MM/DD', I suspect you want
AND to_date( sm.semester_date || '/' || cp.start_year, 'MM/DD/YYYY' ) >=
to_date( '06/01/2011', 'MM/DD/YYYY' )

Answer 4

Your first TO_DATE() relies in the system's default format. Provide a second argument with a proper format string, such as 'MM/DD/YYYY'. Please compare:
SELECT SEMESTER_DATE || START_YEAR AS BARE_STRING, TO_DATE(SEMESTER_DATE || START_YEAR) AS CASTED_TO_DATE
FROM (
SELECT '12/31' AS SEMESTER_DATE, 2010 AS START_YEAR
FROM DUAL
);
SELECT SEMESTER_DATE || START_YEAR AS BARE_STRING, TO_DATE(SEMESTER_DATE || START_YEAR, 'MM/DD/YYYY') AS CASTED_TO_DATE
FROM (
SELECT '12/31' AS SEMESTER_DATE, 2010 AS START_YEAR
FROM DUAL
);