[PHP] Checking for Overlapping Dates

[Thomas . Churm]

Hi, 

Background: 
================

I've created a vacation-request application for our company's intranet. 
When an employee requests a vacation, he has to list the name of another 
employee who will 'fill in' for him while he is gone. 

Before a vacation request can be saved in MySQL, I need to check to make 
sure that the person listed as the employee's replacement during this time 
has not already requested a vacation during the same time period...to 
check to be sure that the two vacation periods do not overlap. 

Date Ranges: 
================

I have fields saved in MySQL called unixStartDate & unixEndDate that are 
unix timestamps for the first day of the employee's vacation and the last 
day of the emplosyee's vacation. 

I have tried to do a check using purely SQL, but this doesn't account for 
all possibilities of overlapping dates: 

(unixStartDate is the unix timestamp for the replacement, whereas the PHP 
var $unixStartDate is the unix timestamp for the employee who wants to 
post a new vacation request) 

$checkSQL = "SELECT * from $DB_TBLName WHERE 
(Trim(WorkerEmail)='$userReplacementEmail') 
AND (Status < 40) 
AND 
( 
( 
($unixStartDate = unixStartDate) 
) 
OR 
( 
($unixEndDate = unixEndDate) 
) 
OR 
( 
($unixStartDate = unixEndDate) 
) 
OR 
( 
($unixEndDate = unixStartDate) 
) 
OR 
( 
(unixStartDate < $unixStartDate) && (unixEndDate > $unixEndDate) 
) 
OR 
( 
(unixStartDate > $unixStartDate) && (unixEndDate < $unixEndDate) 
) 
) 
"; 

So I think what I instead need to do is use PHP code instead of SQL to 
check for overlapping dates in the 2 date ranges I have. 
My two ranges would be like this: 

Replacement's Date Range: 
================
$unixStartDateReplacementVacation 
...to... 
$unixEndDateReplacementVacation 

Employee's Date Range: 
================
$unixStartDateEmployeeVacation 
...to.. 
$unixEndDateEmployeeVacation 


================

...so i need to check that none of the dates occuring in the first date 
range listed above appear in the second date range. 
unfortunately, i have no basic idea of how i should go about doing 
this...should i use arrays of dates, for-loops, or what? 
thanks a whole lot in advance, 

Tom