sql help $result=mysql_query($sql,$conn); <<===ถูกหรือไม่คะ ต้องใส่เป็นอะไร

<?php
$hostname = "127.0.0.1";
$database = "electricityprepaid";
$username = "root";
$password = "root";
$pre_qry = 'SET NAMES TIS620';

//$meatestbank = mysql_pconnect($hostname_meatestbank, $username_meatestbank, $password_meatestbank) or die(mysql_error());
$conn = mysql_connect($hostname, $username, $password);
//mysql_select_db($database,$conn); 
echo $user=$_POST[user];	echo "<br>";
echo $amonut=$_POST[amount];	echo "<br>";
//echo $userid=$_SESSION[userID];

//include ('config.inc.php');
$sql="UPDATE amount
SET amount='$amonut'
WHERE username='$user'";

$result=mysql_query($sql,$conn); <<===ถูกหรือไม่คะ ต้องใส่เป็นอะไร
?>