convert date in sql to compare dates - php

Question

retrieving items from table that fall between a date range.
the date (db table field name is called: submission_date) is being stored in the database as d-M-y (ex: 21-Dec-10)
This is being stored in an oracle database, as sysdate. (it needs to stay in the database as that format, so changing the format of how it is stored is not an option)
I want to convert 21-Dec-10 to 20101221, so I can compare it to date the user has posted, which are two values, end_date, begin_date
All I need is to properly convert submission_date to Ymd (20101221)
below is in theory what I want to do:
select
*
from
table
where
(convert(Ymd=>submission_date) >= $begin_date
AND
convert(Ymd=>submission_date) <= $end_date)

Answer 1

If the column submission_date is of DATE datatype and $begin_date and $end_date are strings of yyyymmdd format then you could use the following query to retrieve rows that fall between a date range:
SELECT *
FROM tab
WHERE submission_date BETWEEN
TO_DATE ( $begin_date, 'yyyymmdd') AND
TO_DATE ( $end_date, 'yyyymmdd');
By not applying a function on submission_date, we give Oracle a chance to use an index on that column, if an index exists.

Answer 2

When you said,
This is being stored in an oracle database, as sysdate.
To me that's saying that the datatype of the column is DATE.
First let's disabuse you of the notion that DATE is stored in a String FORMAT inside Oracle. This is completely erroneous.
If the datatype of the column is DATE then the actual value is stored using 7bytes but can be thought of as a number. The fact that when you query it to examine the value you see a dd-mon-yy format is a function of NLS settings or client options. Remember Oracle is a server, any tool that let's you look at the information stored there is a portal to that info. In other words, you're not really looking at the data, you're looking at something that went and got the data and then put it on the screen for you to see. make sense?
Ok so now that you know there's no such thing as DATE's stored in a certain format, DATE MATH becomes simple.
SELECT Submission_date FROM tab
Returns a date formatted as a string based on client settings or NLS settings.
SELECT Submission_date - 1 FROM tab
Returns a date which is the same time of day, one day earlier
Notice I didn't have to do crazy things to the number 1 to perform date math and that's because the date datatype supports math processing that works like it's a number so subtraction is a simple thing.
If your variables of $begin_date are passed to Oracle as dates then they too need nothing done to them because again, they can be used like numbers.
WHERE Submission_date BETWEEN $Begin AND $End will work.
Bonus Material
BETWEEN is inclusive on both ends.
More Bonus Material
A date is actually stored like this:
Byte 1 -> Century
Byte 2 -> Year
Byte 3 -> Month
Byte 4 -> Day
Byte 5 -> Hour
Byte 6 -> Minute
Byte 7 -> Second
This allows for extremely broad ranges of dates to be supported. It's really the date math library that can make that datatype do cool things like add leap years and get the conversion from Julian to Gregorian and such.
Bonus Material Redux
SQL Server stores dates as two 4 byte integers packed together into a BINARY(8). The first 4-bytes are the elapsed days since SQL Server's base date of 1/1/1900. The Second 4-bytes Store the Time of Day Represented as the Number of Milliseconds After Midnight in quanta of 3.33 milliseconds.
It's a mistake to assume that if the value can be stored, the RDBMS supports it. I believe that SQL Server doesn't handle BC dates at all nor does it handle dates well into the future a la the year 9999. MSSS2008 did introduce a new datatype to deal with those large dates.