How can I prevent database being written to again when the browser does a reload/back?

Question

I\'m putting together a small web app that writes to a database (Perl CGI & MySQL). The CGI script takes some info from a form and writes it to a database. I notice, h

Answer 1

First of all, you can't trust the browser, so any talk about using POST rather than GET is mostly nerd flim-flam. Yes, the client might get a warning along the lines of "Did you mean to resubmit this data again?", but they're quite possibly going to say "Yes, now leave me alone, stupid computer".

And rightly so: if you don't want duplicate submissions, then it's your problem to solve, not the user's.

You presumably have some idea what it means to be a duplicate submission. Maybe it's the same IP within a few seconds, maybe it's the same title of a blog post or a URL that has been submitted recently. Maybe it's a combination of values - e.g. IP address, email address and subject heading of a contact form submission. Either way, if you've manually spotted some duplicates in your data, you should be able to find a way of programmatically identifying a duplicate at the time of submission, and either flagging it for manual approval (if you're not certain), or just telling the submitter "Have you double-clicked?" (If the information isn't amazingly confidential, you could present the existing record you have for them and say "Is this what you meant to send us? If so, you've already done it - hooray")