PHP连接数据库无法修改，如何解决？

问题遇到的现象和发生背景

PHP语言与数据库建立连接，使用form表单进行提交，却无法获取id的值

用代码块功能插入代码，请勿粘贴截图
html>
<html>
    <head>
        <meta charset="utf-8">
        <title>员工信息更新页面title>
        <style type="text/css">
         *{
          margin: 0px;
          padding: 0px;
         }
         div{
          border:2px solid aquamarine;
          width:450px;
          height:350px;
          margin: 0px auto;
          margin-top: 150px;
         }
         p{
          text-align: center;
          background-color: aquamarine;
          font-size: 20px;
          color: black;
         }
         .instr{
          vertical-align: top;
         }
         form{
          margin-top: 25px;
         }
         table{
          margin-left: 5px;
         }
         td{
          text-align:center;
         }
         textarea{
          width: 160px;
          height: 100px;
         }
         input{
          margin: 0px auto;
          margin-top: 5px;
         }
        style>
    head>
    <body>
    <div>
     <p>更新员工信息p>
     <form action="BigProjectDBUpdateOK.php" method="get">
        <table>
        <tr>
         <td><input type="text" name="id" value="$arr['id']?>" placeholder="请输入您想要修改的编号">
         <br />
         td>
        tr>
       table>
       <table>
        <tr>
         <td>姓       名：td>
         <td><input type="text" name="name" value="$arr['name']?>" placeholder="请输入您想要修改的真实姓名">
         <br />
         td>
        tr>
       table>
       <table>
       <tr>
        <td>所属部门：td>
        <td><input type="text" name="dept" value="$arr['dept']?>" placeholder="请输入您想要修改的所属部门">
        <br />
        td>
       tr>
      table>
      <table>
       <tr>
        <td>出生日期：td>
        <td><input type="text" name="birth" value="$arr['birth']?>" placeholder="请输入您想要修改的出生日期">
        <br />
        td>
       tr>
      table>
      <table>
       <tr>
        <td>入职时期：td>
         <td><input type="text" name="worktime" value="$arr['worktime']?>" placeholder="请输入您想要修改的入职时期">
            br>
          td>
         tr>
        table>   
      <table>
            <td>       
                        
                        
                        
                 <a href="BigProjectDBUpdateOK.php"><input type="submit" name="submit" value="修改"/>a>
            td>
      table>
     form>
    div>
  body>
html>



'localhost','root','root','phptest');
    $id=$_GET['id'];
    echo $id;
    $name=$_GET['name'];
    //echo $name;
    $dept=$_GET['dept'];
    //echo $dept;
    $birth=$_GET['birth'];
    //echo $birth;
    $worktime=$_GET['worktime'];
    //echo $entry;
    $query="UPDATE `employee` SET `name`='$name',`dept`='$dept',`birth`='$birth',`worktime`='$worktime' WHERE `id`=$id";
             // UPDATE `employee` SET `姓名`=[value-2],`所属部门`=[value-3],`出生日期`=[value-4],`入职时间`=[value-5] WHERE 1
    echo $query;
    /* $res=mysqli_query($link,$query);
     if($res){
         echo "