wpdb-＆gt;获取行选择（非常复杂）查询无法正常工作

Question

请有人告诉我这个数据库查询有什么错误？它不想为某事工作：S

这是完整的功能：

function foglaltautok(){

    global $wpdb;

    $carname     = $_POST['car-model'];
    $pickupdate  = $_POST['pick-up-date'];
    $dropoffdate = $_POST['drop-off-date'];
    $days        = (strtotime($dropoffdate) - strtotime($pickupdate)) / (60 * 60 * 24)+1;

    $foglaltvagynem = $wpdb->get_row("SELECT carmodel 
        FROM autofoglalt 
        WHERE carmodel = $carname 
            && ($pickupdate BETWEEN  pickupdate AND  dropoffdate 
            OR $dropoffdate BETWEEN  pickupdate AND  dropoffdate 
            OR pickupdate   BETWEEN $pickupdate AND $dropoffdate 
            OR dropoffdate  BETWEEN $pickupdate AND $dropoffdate)"); 

    if(null!==$foglaltvagynem) {
        echo 'error';   
    }
    else 
        if(null === $foglaltvagynem) {
            $wpdb->insert('autofoglalt', array(
                'carmodel'    => $carname,
                'pickupdate'  => $pickupdate,
                'dropoffdate' => $dropoffdate,
                'napok'       => $days
            ));
        }

    die();
}

这部分不起作用：S：

$foglaltvagynem = $wpdb->get_row("SELECT carmodel 
    FROM autofoglalt 
    WHERE carmodel = $carname 
    && ($pickupdate     BETWEEN  pickupdate AND  dropoffdate 
        OR $dropoffdate BETWEEN  pickupdate AND  dropoffdate 
        OR pickupdate   BETWEEN $pickupdate AND $dropoffdate 
        OR dropoffdate  BETWEEN $pickupdate AND $dropoffdate)"
    );

我将此代码写入Car Rental页面，并且通过此查询我想知道，所选CAR是免费的或保留的 - 从选定的pickdate到选定的dropoffdate ..-所以它已经在数据库，或不？ ：）