Help with date column

Question

I have a Table xyz with the following columns:
sdate DATE
count_views NUMBER(20)
The table was created by someone about 1.5 years back. It contains data from the month of june, 2009 till date.
When I run a query on it:
SELECT DISTINCT sdate FROM xyz WHERE (sdate) BETWEEN TO_DATE('01-JAN-09') AND TO_DATE('31-DEC-09');
I get the result as:
sdate
30-NOV-09
31-DEC-09
However when I modify the query to:
SELECT DISTINCT sdate FROM xyz WHERE TO_DATE(sdate) BETWEEN TO_DATE('01-JAN-09') AND TO_DATE('31-DEC-09');
I get the result as:
sdate
30-JUN-09
30-JUL-09
30-AUG-09
30-SEP-09
30-OCT-09
30-NOV-09
31-DEC-09
Can someone please tell what the issue might be with the table?

Answer 1

There's nothing wrong with the table and everything wrong with your query.
First of all, when you do "to_date(<string>)", you're relying on the default nls_date_format to work out what the format of that string is. If the two do not coincide, you have just made a bug. ALWAYS be explicit and code a format mask, eg:
TO_DATE('01-JAN-09', 'dd-MON-rr')Or, even better:
TO_DATE('01/01/2009', 'dd/mm/yyyy')
-- this has an explicit 4-digit year
-- it's also nls-independent (doesn't matter if your database/client is french, italian, english, etc, it'll work. Coding the month as JAN etc will error if you're working in French, for example).As for to_dating something that is already a date? BAD BAD BAD idea!
What happens is you force the date to be implicitly converted a string via the default format mask, then you force another implicit conversion to a date. It's a rotten way of doing something, and can lose information, such as the initial two digits of the year if your default mask is DD-MON-YY.
NEVER to_date something that is already in date format (and correspondingly, never to_timestamp a timestamp!). That way madness lies!