$hostname = "localhost";
$username = "db_username";
$password = "db_password";
$database = "db_name";

mysql_connect($hostname, $username, $password);

// The find and replace strings.
$find = "find_this_text";
$replace = "replace_with_this_text";

$loop = mysql_query("
    SELECT
        concat('UPDATE ',table_schema,'.',table_name, ' SET ',column_name, '=replace(',column_name,', ''{$find}'', ''{$replace}'');') AS s
    FROM
        information_schema.columns
    WHERE
        table_schema = '{$database}'")
or die ('Cant loop through dbfields: ' . mysql_error());

while ($query = mysql_fetch_assoc($loop))
{
        mysql_query($query['s']);
}