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這個技巧的主要原理是不允許用戶回退后再次提交，也就是說回退后修改再提交也是不允許的，而且也不能避免Ctrl-C/Ctrl-V的灌水辦法。究竟有沒有用，還是看各位站長的喜好了
你是否遇到過“重復提交”的問題？要解決這個問題其實并不難。這里有一個簡單的方法避免同一表單的重復提交。 
首先，我們可以定義一個session變量用來保存一個表單的提交序列號。這里我定義為“$userLastAction”。然后在表單里加入一個hidden變量，把值設為$userLastAction+1： 
<input type=Hidden name=lastAction value=<? =$userLastAction+1 ?>> 
最后，在處理提交之前判斷表單是否已被提交過： 
if($lastAction>$userLastAction and inputIsValid(...)){ 
$userLastAction++; // 序列號加1 
// 處理表單數據 
}

原文： 
Avoid multiple form submissions 
Submitted By: Douglas E. Cook 
Date: 07/26/00 19:46 
Does your database suffer from "duplicate post" syndrome? The cure isn't too difficult. Here is a simple way to prevent users from submitting the same form multiple times.

First, declare a session variable to store a serial number for each form. I call mine "$userLastAction." Then, in every form where duplicate submission is a problem, include a hidden field, and set the value to $userLastAction+1:

<INPUT TYPE=HIDDEN NAME=lastAction VALUE=<?= $userLastAction+1 ?>>

Finally, verify that the form has not been previously submitted before acting on the submission:

if($lastAction>$userLastAction and inputIsValid(...)){ 
$userLastAction++; // Increment serial number 
// Act on form here 
}