Help with Date Range

Question

Hi,
I have an Oracle form which allows users to enter :start_date_active(mandatory) and :end_date_active (can be null).
I need to check in form using SQL if there already exists a record for this date range or if there is any overlapping date ranges for the value entered and disallow user from entering that.
I have my query as follows:
SELECT (1)
FROM <table> xsv
WHERE 1=1
AND ( (:START_DATE_ACTIVE >= xsv.start_date_active) AND
(:START_DATE_ACTIVE <= nvl(xsv.end_date_active,'31-DEC-4712'))
OR
     (:END_DATE_ACTIVE >= xsv.start_date_active) AND
(:END_DATE_ACTIVE <= nvl(xsv.end_date_active,'31-DEC-4712'))
But, this incorrectly allows me to enter over lapping date ranges when the :end_date_active is null.
It should work as follows :
eg.
start_date_active end_date_active
01-Apr-2009 allowed
01-Mar-2009 10-Mar-2009 allowed
01-feb-2009 Not allowed, as it overlaps with 1st record
10-feb-2009 05-Mar-2009 Not allowed, as it overlaps with 2nd record
05-Mar-2009 20-mar-2009 Not allowed, as it overlaps with 2nd record
and so on.
How do I modify my query to deal with null end dates ?
Many Thanks
Shankar

Answer 1

Hi, Shankar,
Whenever you have a question, it helps to post:
(1) The version of Oracle (and any other relevant software) you're using
(2) A little sample data (just enough to show what the problem is) from all the relevant tables
(3) The results you want from that data (You posted this. It would be better if it were formatted.)
(4) Your best attempt so far (formatted) (You posted this, but since it's unformated, it's very hard to read.)
(5) The full error message (if any), including line number
Executable SQL statements (like "CREATE TABLE AS ..." or "INSERT ..." statements) are best for (2).
Formatted tabular output is okay for (3). Type these 6 characters
&#123;code&#125;
(small letters only, inside curly brackets) before and after formatted text, to preserve spacing.
Use different names for the parameters and the columns. For example, if the column is called start_date_active, call the corresponding parameter :p_start_date_active. It will help to keep them straight.
In this statement, if the column end_date_active IS NULL, you're treating it as an impossibly late date:
(:END_DATE_ACTIVE <= nvl(xsv.end_date_active,'31-DEC-4712'))That's good. (You should really use TO_DATE ('31-DEC-4712', 'DD-MON-YYYY'), though.)
If it's possible for the parameter :end_date_active to be NULL, you should use NVL in the same way, to equate it with some appropriate date.
The correct way to see if the range a to b (a <= b) overlaps with x to y (x <= y) is:
WHERE   b >= x
AND     a <= yIf you want an expression that's TRUE when they do not overlap, then say
WHERE   NOT (    b >= x
            AND  a <= y
            )or, equivalently,
WHERE   b < x
OR      a > y