如果条目不存在，则将条目添加到数据库中

i'm currently trying to work through a problem where an entry gets added into a database if it doesn't exist. However if it does and the username matches one of the database, it gets updated to whatever the other inputs are. However I am currently getting the error:

sqlsrv_num_rows() expects parameter 1 to be resource

My code is shown below:

 $describeQuery = ("INSERT INTO User 
                  (userID, first_name, last_name)
                   VALUES ('".$Username."', '".$FirstName."', '".$LastName."');");
 $results = sqlsrv_query($conn, $describeQuery);
 if(sqlsrv_num_rows($describeQuery) == 0)
        {
            echo 'New entry added';
        }
        else
        {                   
            $describeQuery2= ("UPDATE User 
                             SET first_name = '".$FirstName."',
                             last_name = '".$LastName."' 
                             WHERE userID = '".$Username."'");
            $results = sqlsrv_query($conn, $describeQuery2);

            $describeQuery3= ("UPDATE Current_Location 
                             SET first_name = '".$FirstName."',
                             last_name = '".$LastName."' 
                             WHERE userID = '".$Username."'");
            $results = sqlsrv_query($conn, $describeQuery3);            

            echo '<br>';
            echo '<br>';
            echo 'Entry updated';

Any help would be appreciated.