问如何让生成的代码在几次输入(PHP)后失效？

EN

<?php
include("ProcessCode.php"); 
$con = mysqli_connect("localhost","root","") ;
if(mysqli_select_db($con,"login"))
{
echo 'database  selected' ;
}

$rand=rand();
echo $rand ;

$sql = "INSERT INTO random (number) VALUES ('$rand') "  ;

if(mysqli_query($con,$sql))
{
   echo 'inserted'  ;
}

?>
    $CodeCheck=$_POST['code'];

     //Establishing Connection with server
     $conn = mysqli_connect("localhost", "root", "");

      //Selecting Database
      $db = mysqli_select_db($conn, "login");

       //sql query to fetch information of registerd user and finds user match.
      $query = mysqli_query($conn, "select * from random WHERE number='$CodeCheck'");

       $rows = mysqli_num_rows($query);

      if (mysqli_num_rows($query) > 0)
         {
          echo " Code exists already.";
         }

      if($rows == 1)
       {
        header("Location: Success.php");

       }
     else
     {
      $error = " Code is Invalid";
      echo $error;
     }