<?php
$query = $db->prepare("INSERT INTO dolar SET alis = ?,satis =?");
$insert = $query->execute(array($usd_buying, $usd_selling));
$insert2 = $query->execute(array($euro_buying, $euro_selling));
$insert3 = $query->execute(array($kdolar_buying , $kdolar_selling));
if ( $insert && $insert2 && $inster3 ){
    $last_id = $db->lastInsertId();
    print "Kayıt işlemi başarılı!";
}
?>