Php 插入前检查重复项-错误消息

我想在插入查询中添加第三条错误消息。 目前我有“代码有效”和“代码无效”，我不知道该怎么做才能添加第三条错误消息，该消息将显示在重复代码上

不管怎样，这是我的代码

    <?php
if(isset($_POST['submit'])){
   if (strlen($_POST['coda']) == 12 && substr($_POST['coda'],0,1) == '0'){
      $code = $_POST['coda'];
      $remote_addr = $_SERVER['REMOTE_ADDR'];
         $secret = $_POST['secret'];
      $select_query = mysql_query("SELECT * FROM table WHERE code = '$code' OR ip = '$remote_addr'");
      if(mysql_num_rows($select_query) == 0){
         mysql_query("INSERT INTO table(code,secret,ip,date,used,status) VALUES('$code','$secret','$remote_addr',CURDATE(),'n','pending')");

      }
      Print "<font color='green'>VALID CODE</font>"; 
} else { 

Print "<font color='red'>INVALID CODE</font>"; 
}

}?>

编辑：

---

我不确定是否理解你的问题，但以下是我的想法：

<?php
if(isset($_POST['submit'])){
   if (strlen($_POST['coda']) == 12 && substr($_POST['coda'],0,1) == '0'){
      $code = $_POST['coda'];
      $remote_addr = $_SERVER['REMOTE_ADDR'];
      $secret = $_POST['secret'];
      if(mysql_num_rows(mysql_query("SELECT * FROM table WHERE code = '$code'")) > 0) {
         Print "<font color='red'>DUPLICATE CODE</font>";
      } else {
         $select_query = mysql_query("SELECT * FROM table WHERE code = '$code' OR ip = '$remote_addr'");
         if(mysql_num_rows($select_query) == 0){
            mysql_query("INSERT INTO table(code,secret,ip,date,used,status) VALUES('$code','$secret','$remote_addr',CURDATE(),'n','pending')");
            Print "<font color='green'>VALID CODE</font>"; 
         }
      }
   } else { 
      Print "<font color='red'>INVALID CODE</font>"; 
   }
}
?>

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我已经编辑了我的第一篇文章，希望能让它更清晰。你想检查一下你的数据库中是否已经使用了该代码，对吗？如果你已经找到答案，请将你的解决方案作为答案发布。@deceze我试过了，但我做不到。我确实要等8个小时，因为我还没有100个代表。我会尽快把它寄出去。
<?php
if(isset($_POST['submit'])){
   if (strlen($_POST['coda']) == 12 && substr($_POST['coda'],0,1) == '0'){
      $code = $_POST['coda'];
      $remote_addr = $_SERVER['REMOTE_ADDR'];
      $secret = $_POST['secret'];
      if(mysql_num_rows(mysql_query("SELECT * FROM table WHERE code = '$code'")) > 0) {
         Print "<font color='red'>DUPLICATE CODE</font>";
      } else {
         $select_query = mysql_query("SELECT * FROM table WHERE code = '$code' OR ip = '$remote_addr'");
         if(mysql_num_rows($select_query) == 0){
            mysql_query("INSERT INTO table(code,secret,ip,date,used,status) VALUES('$code','$secret','$remote_addr',CURDATE(),'n','pending')");
            Print "<font color='green'>VALID CODE</font>"; 
         }
      }
   } else { 
      Print "<font color='red'>INVALID CODE</font>"; 
   }
}
?>