Error in Oracle TO_CHAR() Function

Question

Why does the following error occur on Line 7 of the query below?

Error: ORA-01861: literal does not match format string

Query:

01: SELECT hour
02: FROM (WITH all_hours AS
03:             (SELECT TO_DATE ('2000-01-01', 'yyyy-mm-dd') 
04:                      + NUMTODSINTERVAL (LEVEL - 1, 'hour') hour
05:              FROM DUAL
06:              CONNECT BY LEVEL <= 1000000)
07:      SELECT TO_CHAR (h.hour, 'yyyy-mm-dd hh:mi am') hour
08:      FROM all_hours h
09:      GROUP BY h.hour)
10: WHERE hour BETWEEN TO_DATE ('2009-11-10 01:00 am', 'yyyy-mm-dd hh:mi am')
11:                AND TO_DATE ('2009-11-10 01:00 am', 'yyyy-mm-dd hh:mi am')

Answer 1

Well, it is not on the line 7. Problem is that "hour" on some level is converted to string (to_char), but after that is compared to the date, and implicit conversion does not work always. Corrected query:

SELECT hour
FROM (WITH all_hours AS
            (
            SELECT TO_DATE ('2000-01-01', 'yyyy-mm-dd') 
                     + NUMTODSINTERVAL (LEVEL - 1, 'hour') hour
             FROM DUAL
             CONNECT BY LEVEL <= 1000000
             )
     SELECT TO_CHAR (h.hour, 'yyyy-mm-dd hh:mi am') hour, h.hour as hourdate
     FROM all_hours h
     GROUP BY h.hour)
WHERE hourdate BETWEEN TO_DATE ('2009-11-10 01:00 am', 'yyyy-mm-dd hh:mi am')
               AND TO_DATE ('2009-11-10 01:00 am', 'yyyy-mm-dd hh:mi am')

Answer 2

Hi Steven,

you're comparing DATEs to CHARs in the WHERE clause. This should work:

SQL> SELECT TO_CHAR(hour, 'yyyy-mm-dd hh:mi am')
  2    FROM (WITH all_hours AS (SELECT TO_DATE('2000-01-01', 'yyyy-mm-dd')
  3                              + NUMTODSINTERVAL(LEVEL - 1, 'hour') hour
  4                               FROM DUAL
  5                             CONNECT BY LEVEL <= 1000000)
  6          SELECT hour FROM all_hours h GROUP BY h.hour)
  7   WHERE hour BETWEEN TO_DATE('2009-11-10 01:00 am', 'yyyy-mm-dd hh:mi am')
  8          AND TO_DATE('2009-11-10 01:00 am', 'yyyy-mm-dd hh:mi am')
  9  ;

TO_CHAR(HOUR,'YYYY-MM-DDHH:MIA
------------------------------
2009-11-10 01:00 am