SQL/PHP: Zahl in Datenbank - Komma durch Punkt

<?php
include ('define.php'); // DB Zugang
for($i=1; $i<19000; $i++)
{
 $sql_plz = mysql_query("SELECT petrol_station_masters.id, petrol_station_masters.longitude AS  longitude, petrol_station_masters.latitude AS latitude FROM petrol_station_masters WHERE petrol_station_masters.id = '".$i."' ") or die(mysql_error());
 echo mysql_num_rows($sql_plz);
 while( $ds3 = mysql_fetch_object($sql_plz) )
 {
 $latitude =$ds3->latitude;
 $longitude = $ds3->longitude;
 $latitude = str_replace(',', '.', $latitude);
 $longitude = str_replace(',', '.', $longitude);
 
 $update = mysql_query("UPDATE petrol_station_masters SET petrol_station_masters.longitude = '".$longitude."' AND petrol_station_masters.latitude = '".$latitude."' WHERE petrol_station_masters.id = "'.$ds3->petrol_station_masters.id.'" ") or die(mysql_error());
 }
}

?>

UPDATE petrol_station_masters SET petrol_station_masters.longitude = REPLACE(petrol_station_masters.longitude, ',', '.') AND petrol_station_masters.latitude = REPLACE(petrol_station_masters.latitude, ',', '.');

UPDATE petrol_station_masters SET petrol_station_masters.longitude_new = REPLACE(petrol_station_masters.longitude, ',', '.') AND petrol_station_masters.latitude_new = REPLACE(petrol_station_masters.latitude, ',', '.');

Die derzeitigen Spalten sind varchar.

Update Tabelle Set Zwischenspalte = Replace(longitude, ',', '.')
Update Tabelle Set longitude_neu = Cast(Zwischenspalte as Decimal(18,14))