Php 无法将生成的随机id插入数据库

我试图通过会话从另一个页面获取随机id的值，但在插入到数据库中时，它并没有被插入到数据库中。它是零，下面是代码：

Stud.php
     <?php  
                session_start();
                $seed = str_split('abcdefghijklmnopqrstuvwxyz1234567890');
                $rand = array_rand($seed, 7);
                $convert = array_map(function($n){
                global $seed;
                return $seed[$n];
                },$rand);
                $var = implode('',$convert);
                echo $var;
                //echo "<blink>Your Complaint is is:".$var."</blink>";
                // $_SESSION['varname'] = $var;
                // unset($comment);

            ?>

Stud.php

Insert.php

---

检查：投诉Id的类型将其更改为varchar（1024）

<?php
session_start();
include 'library/dbconnect.php';
$_SESSION['varname'] = $var;
$var_value = $_SESSION['varname'];$name=$_POST['Studname'];
$district=$_POST['district'];
$school_name=$_POST['School_name'];
$standard=$_POST['std'];
$division=$_POST['Division'];
$complaint=$_POST['Complaint'];
$entryDate=$_POST['date'];
$dateEntry=explode('-',$entryDate);
$date1=$dateEntry[2]."-".$dateEntry[1]."-".$dateEntry[0];
echo $name."<br />".$district."<br />".$date1."<br />";
$query2="INSERT INTO `Complaint_register`(`complain_Id`,`entrydate`, `studname`,
`District`, `School_name`, `Standard`, `Division`, `Complaint`, `status`) VALUES 
('$var_value','$date1','$name','$district','$school_name','$standard',
'$division','$complaint',1)";   
$result2=mysql_query($query2)or die(mysql_error());
$query3="SELECT * FROM Complaint_register";
$result3=mysql_query($query3);
$num=mysql_numrows($result3);
 if($result2)
{
$coment= $num.' Complaint Successfully Registered';
header("Location:stud.php");

}
?>