Editing data from MySQL via PHP

Question

A PHP script that is supposed to allow me to edit certain rows in my MySQL database is giving me a frustrating situation. The database's records are all presented in this file, and it functions exactly as it should.

<table cellpadding="10">
<tr>
<td>ID</td>
<td>First Name</td>
<td>Last Name</td>
<td>E-mail</td>
<td>Phone</td>
</tr>

<?php

$username="username here";
$password="password here";
$database="database name here";

mysql_connect(localhost,$username,$password);
@mysql_select_db($database) or die( "Unable to select database");
$query="SELECT * FROM students";
$result=mysql_query($query);
mysql_close();

while ($row=mysql_fetch_array($result)){
echo ("<tr><td>$row[id]</td>");
echo ("<td>$row[first]</td>");
echo ("<td>$row[last]</td>");
echo ("<td>$row[email]</td>");
echo ("<td>$row[phone]</td>");
echo ("<td><a href=\"StudentEdit.php?id=$row[id]\">Edit</a></td></tr>");
}
echo "</table>";

?>

As you can see, each row has an "Edit" link that is supposed to allow the user to edit that individual student's data. Here, then, is StudentEdit.php:

<?php

$username="username";
$password="password";
$database="database";

mysql_connect(localhost,$username,$password);

$student_id = $_GET[id]; 
$query = "SELECT * FROM students WHERE id = '$student_id'"; 
$result = mysql_query($query);
$row = mysql_fetch_array($result);
mysql_close();
?>

<form method="post" action="EditStudentData.php" />

<table>

<tr>
<td><input type="hidden" name="id" value="<? echo "$row[id]" ?>"></td>
</tr>

<tr>
<td>First Name:</td>
<td><input type="text" name="first" value="<? echo "$row[first]" ?>"></td>
</tr>

<tr>
<td>Last Name:</td>
<td><input type="text" name="last" value="<? echo "$row[last]" ?>"></td>
</tr>

<tr>
<td>Phone Number:</td>
<td><input type="text" name="phone" value="<? echo "$row[phone]" ?>"></td>
</tr>

<tr>
<td>E-mail:</td>
<td><input type="text" name="email" value="<?echo "$row[email]" ?>"></td>
</tr>

</table>

</form>

However, when I do this, I receive the following error message:

/home4/lukaspl1/public html/StudentEdit.php, line 12, MySQL fetch array() warning: given argument is not a valid MySQL result resource.

Any suggestions as to what's wrong and how to repair it?