The Where Clause in MySQL

Code:

$con = mysql_connect("localhost","peter","abc123");
if (!$con)
{
die('Could not connect: ' . mysql_error());
}
mysql_select_db("my_db", $con);
$result = mysql_query("SELECT * FROM Persons WHERE FirstName='Peter'");
while($row = mysql_fetch_array($result))
{
echo $row['FirstName'] . " " . $row['LastName'];
}
?>