tablo 1 = fiyat
tablo 2 = çarpılacak kur fiyatı
SELECT *,(SELECT `fiyat` FROM `urunler` WHERE `kur`=`kuradi` LIMIT 1)*`deger` AS `fastfiyat` FROM `kurlar` ORDER BY `fastfiyat` DESC
SELECT *,(SELECT `deger` FROM `kurlar` WHERE `kuradi`=`kur` LIMIT 1)*`fiyat` AS `fastfiyat` FROM `urunler` ORDER BY `fastfiyat` DESC