COMPARING OBJECTS using PHP's usort() method.PHP and MySQL both provide ways to sort your data already, and it is a good idea to use that if possible. However, since this section is on comparing your own PHP objects (and that you may need to alter the sorting method in PHP), here is an example of how you can do that using PHP's "user-defined" sort method, usort() and your own class compare() methods.<?phpclass Employee{ public $first; public $last; public $emp_id; public function __construct($emp_first, $emp_last, $emp_ID) { $this->first = $emp_first; $this->last = $emp_last; $this->emp_id = $emp_ID; } public static function compare($a, $b) { if ($a->emp_id < $b->emp_id) return -1; else if($a->emp_id == $b->emp_id) return 0; else return 1; } public function __toString() { return "Employee[first=$this->first, last=$this->last, emp_id=$this->emp_id]"; }}$employees = array( new Employee("John", "Smith", 345), new Employee("Jane", "Doe", 231), new Employee("Mike", "Barnes", 522), new Employee("Vicky", "Jones", 107), new Employee("John", "Doe", 2), new Employee("Kevin", "Patterson", 89));usort($employees, array("Employee", "compare"));foreach($employees as $employee){ echo $employee . '<br>';}?>Results are now sorted by emp_id:Employee[first=John, last=Doe, emp_id=2]Employee[first=Kevin, last=Patterson, emp_id=89]Employee[first=Vicky, last=Jones, emp_id=107]Employee[first=Jane, last=Doe, emp_id=231]Employee[first=John, last=Smith, emp_id=345]Employee[first=Mike, last=Barnes, emp_id=522]Important Note: Your PHP code will never directly call the Employee's compare() method, but PHP's usort() calls it many many times. Also, when defining the rules for sorting, make sure to get to a "primitive type" level... that is, down to a number or string, and that the function returns a -1, 0, or 1, for reliable and consistent results.Also see: http://www.php.net/manual/en/function.usort.php for more examples of PHP's sorting facilities.