如何解决php echo乱码问题

<?php
header("Content-Type:text/html;charset=gb2312");
//设置页面字符集
$conn=mysql_connect("localhost", "root", "****");
//****为mysql密码
mysql_select_db("world");
mysql_query("set names utf8");
$sql="select * from city order by population desc";
$res=mysql_query($sql);
echo "<h1>城市信息一览表</h1>";
echo "<table width=&#39;1000px&#39;>";
echo "<tr>";
echo "<td>id</td><td>name</td><td>countrycode</td><td>district</td><td>population</td>";
echo "</tr>";
while($row=mysql_fetch_assoc($res)){
    echo "<tr>";
    echo "<td>{$row[&#39;ID&#39;]}</td><td>{$row[&#39;Name&#39;]}</td><td>{$row[&#39;CountryCode&#39;]}</td><td>{$row[&#39;District&#39;]}</td><td>{$row[&#39;Population&#39;]}</td>";
    echo "</tr>";
}
echo "</table>";
mysql_close($conn);
?>