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
}

譯自：phpbuilder
這只是一個小技巧，用來避免一個表單的重復提交。這樣多少可以防止一些灌水的現象，另外有時候由于網絡狀況等原因用戶不知道提交是否成功，也會再次提交同一份表單。
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。