$Fiyat=$db->prepare("SELECT SUM(sütun_adı) AS takma_ad FROM tablo_adı");
$Fiyat->execute();
$FiyatYaz= $Fiyat->fetch(PDO::FETCH_ASSOC);
<?=$FiyatYaz['takma_ad']?>

<?php
$db = $_SERVER["DOCUMENT_ROOT"] ."/access/dene.mdb";
if (!file_exists($db))
{
       die("No database file.");
}
$baglanti=new PDO("odbc:DRIVER={Microsoft Access Driver (*.mdb)}; DBQ=$db; Uid=; Pwd=;");
$Fiyat=$baglanti->prepare("SELECT SUM(fiyat) AS takma_ad FROM satis");
$Fiyat->execute();
$FiyatYaz= $Fiyat->fetch(PDO::FETCH_ASSOC);
$topla=$FiyatYaz['takma_ad'];
echo $topla;
?>