php+mysql implements authentication code_PHP tutorial

$uname=$_POST["username"];
$pwd=$_POST["password"];
$link = mysql_connect('localhost', 'root', '123456')
or die('Could not connect: ' . mysql_error());
mysql_select_db('ruida') or die('Could not select database');
//Execute SQL query
$query = 'SELECT * FROM user';
$result = mysql_query($query ) or die('Query failed: ' . mysql_error());
while($row=mysql_fetch_array($result)){
if($uname==$row['username'] && $pwd= =$row['password'])
{
//Page jump
}
else
echo 'error!';}
// Release the result set
mysql_free_result($result);
//Close the connection
mysql_close($link);
?>