数据库访问小列题

<select>
<?php
$db=new MySQLi("localhost","root","3177389","my test");

!mysqli_connect_error() or die("连接失败！");
$sql="select*from Nation";

$result=$db->query($sql);
$attr=$result->fetch_all();

for($i=0;$i<count($attr );$i++)
{
    list($code,$name)=$attr[$i];
    
    echo "<option value='{$code}'>{$name}</option>";
    
    
}

?>
</select>

<?php
//造连接对象
$db=new MySQLi("localhost","root","3177389","my test");
//判断是否出错
!mysqli_connect_error()or die ("连接失败!");
//写sql语句
$sql="select *from Info";
//执行sql语句
$result=$db->query($sql);
//处理查询数据并显示
echo "<table width='100%' border='1' cellpadding='0' cellpadding='0'>";

echo "<tr><td>代号</td><td>姓名</td><td>性别</td><td>民族</td ><td>生日</td></tr>";
while($row=$result->fetch_row())

{
    $sex=$row[2]?"男":"女";
    
    $name =ShowNation($db,$row [3]);
    
    echo "<tr><td>{$row[0]}</td><td>{$row[1]}</td><td>{$sex}</td><td>{$name}</td ><td>{$row[4]}</td></tr>";
    
    
}
echo "</table >";


function showNation ($db,$code)

{
    
        $sql = "select Name from Nation where Code='{$code}'";
        $result=$db->query($sql);
        
        
        $jieguo =$result ->fetch_row();
        
        return $jieguo[0];
}
?>

<form action="0324chili.php" method="post">
<div>
        用户名：
        <input type="text" name="zw" />
    </div>
    <div>
        密码：
        <input type="text" name="pwd" />
    </div>
    <div>
        <input type="submit" value="登录" />
    </div>



</form>

<?php

$uid=$_POST["zw"];
$pwd=$_POST["pwd"];

$db=new MySQLi("localhost","root","3177389","my test");

!mysqli_connect_error()or die ("连接失败！");

$sql="select count(*) from login where username='{$uid}' and  password='{$pwd}'";

$resul=$db->query($sql);
$attr=$resul->fetch_row();

if($attr[0] == 1)
{
    header("location:zhu.php");
}
else
{
    header("location:denglu.php");
}