PHP 怎么修改这段代码 让下拉菜单点击提交后可以跳转到相应页面

<?php
    $link = mysqli_connect('localhost','root','root','db_chengji','3306');
    mysqli_set_charset($link,'utf8');
    $sql1 = "select * from `tb_info` ORDER BY `id` ASC ";
    $mysqli_result1 = mysqli_query($link,$sql1);
    $recount = mysqli_num_rows($mysqli_result1);
    $pagesize = 7;
    $pageno = $_GET['pageno'] ? $_GET['pageno'] : 1;
    $pagecount = ceil($recount / $pagesize);
    $offset = ($pageno-1) * $pagesize;
    $sql = "select * from `tb_info` ORDER BY `id` ASC limit $offset,$pagesize";
    $mysqli_result1 = mysqli_query($link,$sql);
    echo "<table align='center' border='1' style='border-collapse: collapse' width='450'>";
    echo "<tr>";
    while($field = mysqli_fetch_field($mysqli_result1))
        echo "<th>".$field->name."</th>";
    echo "</tr>";
    $j = 0;
    while($row = mysqli_fetch_object($mysqli_result1)) {
        $j++;
        echo "<tr>";
        echo "<td>" . $row->id . "</td>";
        echo "<td>" . $row->name . "</td>";
        echo "<td>" . $row->sex . "</td>";
        echo "<td>" . $row->class . "</td>";
        echo "<td>" . $row->hobby . "</td>";
        echo "</tr>";
    }

    for($i = $j;$i<$pagesize;$i++){
        echo "<tr>";
        echo "<td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td>";
        echo "</tr>";

    }
    $arr=array();
    echo "<tr><th colspan='5'>";
    for($pageno = 1;$pageno <= $pagecount;$pageno ++){
        echo "<a href='?pageno=$pageno'>$pageno</a>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;";
        $arr[]=$pageno;
    }
    //print_r($arr);
    echo "<select name='sel'>";
    foreach($arr as $key=>$value){
        echo "<option value=\"key\">第{$value}页</option>";
    }
    echo"<form name='form1' method='post' action=''>
            <input type='submit' name='bt' value='提交' >
            <a href='?pageno=$pageno'>
        </form>";
    if(isset($_POST['bt']))
        
echo "</select>";
    echo "</th></tr>";
    echo "</table>";

看了一下，主要是两个问题：
1、select下拉选择放在form表单外边了，导致下单选择的信息没有正常提交；
2、表单用的是POST提交，上边开头没有写接收POST表单信息。
以下是我改过之后代码，你试一下：

<?php
    $link = mysqli_connect('localhost','root','root','db_chengji','3306');
    mysqli_set_charset($link,'utf8');
    $sql1 = "select * from `tb_info` ORDER BY `id` ASC ";
    $mysqli_result1 = mysqli_query($link,$sql1);
    $recount = mysqli_num_rows($mysqli_result1);
    $pagesize = 7;
    //检测提交类型 POST/GET
    $pagenoType = isset($_POST['sel'])?$_POST['sel']:$_GET['pageno'];
    $pageno = $pagenoType ? $pagenoType : 1;
    $pagecount = ceil($recount / $pagesize);
    $offset = ($pageno-1) * $pagesize;
    $sql = "select * from `tb_info` ORDER BY `id` ASC limit $offset,$pagesize";
    $mysqli_result1 = mysqli_query($link,$sql);
    echo "<table align='center' border='1' style='border-collapse: collapse' width='450'>";
    echo "<tr>";
    while($field = mysqli_fetch_field($mysqli_result1))
        echo "<th>".$field->name."</th>";
    echo "</tr>";
    $j = 0;
    while($row = mysqli_fetch_object($mysqli_result1)) {
        $j++;
        echo "<tr>";
        echo "<td>" . $row->id . "</td>";
        echo "<td>" . $row->name . "</td>";
        echo "<td>" . $row->sex . "</td>";
        echo "<td>" . $row->class_name . "</td>";
        echo "<td>" . $row->hobby . "</td>";
        echo "</tr>";
    }
 
    for($i = $j;$i<$pagesize;$i++){
        echo "<tr>";
        echo "<td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td><td>&nbsp;</td>";
        echo "</tr>";
 
    }
    $arr=array();
    echo "<tr><th colspan='5'>";
    for($pageno = 1;$pageno <= $pagecount;$pageno ++){
        echo "<a href='?pageno=$pageno'>$pageno</a>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;";
        //使数组的键名与值相同
        $arr[$pageno]=$pageno;
    }
    //print_r($arr);
    echo"<form name='form1' method='POST' action=''>";
    echo "<select name='sel'>";
    foreach($arr as $key=>$value){
        if(isset($_POST['sel']) && !empty($_POST['sel']) && $value == $_POST['sel']){
            echo "<option value=\"$key\" selected='selected'>第{$value}页</option>";
        }else{
            echo "<option value=\"$key\">第{$value}页</option>";        
        }
    }
    echo "<input type='submit' name='bt' value='提交' >
            <a href='?pageno=$pageno'>
        </form>";
    if(isset($_POST['bt']))
        
    echo "</select>";
    echo "</th></tr>";
    echo "</table>";
?>