Stored Procedure To Check Date Range

Hi guys,
I have written a stored procedure to check for date range, say if the user enters a value for 'city-from' , 'city-to', 'start-date' and end-date, this stored procedure should verify these 2 dates against the dates stored in the database. If these 2 dates had already existed for the cities that they input, the stored procedure should return 1 for the PIsExists parameter. Below's how I constructed the queries:  1 ALTER PROCEDURE dbo.DateCheck
2 @PID INTEGER = -1 OUTPUT,
3 @PCityFrom Char(3) = '',
4 @PCityTo Char(3) = '',
5 @PDateFrom DATETIME = '31 Dec 9999',
6 @PDateTo DATETIME = '31 Dec 9999',
7 @PIsExists BIT = 1 OUTPUT
8 AS
9
10 CREATE TABLE #TmpControlRequst
11 (
12 IDINTEGER,
13 IsExistsCHAR(1)
14 )
15 /*###Pseudo
16 1. Check the Date From and Date To
17 -- select all the value equal to parameter cityFrom and cityTo
18 -- insert the selection records into tmp table
19 --*/
20 INSERT INTO #TmpControlRequst
21 (ID, IsExists)
22 SELECT ID,
23 IsExists = CASE WHEN DateFrom <> '31 Dec 9999' AND DateTo <> '31 Dec 9999'
24 AND @PDateFrom <= DateFrom AND @PDateFrom <= DateTo
25 AND @PDateTo >= DateFrom AND @PDateTo <= DateTo THEN 1
26 WHEN DateFrom <> '31 Dec 9999' AND DateTo <> '31 Dec 9999'
27 AND @PDateFrom >= DateFrom AND @PDateFrom <= DateTo
28 AND @PDateTo >= DateFrom AND @PDateTo <= DateTo THEN 1
29 WHEN DateFrom <> '31 Dec 9999' AND DateTo <> '31 Dec 9999'
30 AND @PDateFrom >= DateFrom AND @PDateFrom <= DateTo
31 AND @PDateTo >= DateFrom AND @PDateTo >= DateTo THEN 1
32 WHEN DateFrom <> '31 Dec 9999' AND DateTo <> '31 Dec 9999'
33 AND @PDateFrom <= DateFrom AND @PDateFrom <= DateTo
34 AND @PDateTo >= DateFrom AND @PDateTo >= DateTo THEN 1
35 ELSE 0 END
36 FROM RequestTable
37 WHERE ID <> @PID
38 AND CityFrom = @PCityFrom
39 AND CityTo = @PCityTo
40
41 --======== FINAL RESULT
42 -- For tmp table:-
43 -- isExists = 1 ==> date lapse
44 -- isExists = 0 ==> date ok
45 -- if count for (isExists = 1) in tmp table is > 0 then return 1 and data not allow for posting
46 SELECT @PIsExists = CASE WHEN COUNT(*) > 0 THEN 1
47 ELSE 0 END
48 FROM #TmpControlRequst
49 WHEREIsExists = 1
50
51 SELECT @PIsExists
52 --=========
53
54 DROP TABLE #TmpControlRequst
55
56 --=========
57 RETURN(0)However, when I run this stored procedure, 'PIsExists' would always return -1. I am positive that the values that I passed in, had already existed in the database. Any idea what might be causing this problem? Thanks in advance