Hello, I wanted to set up a downloads counter on my web, and in order to do that I want to use onClick action that will access SQL and add one to the counter. Now here is the problem.
how do I execute php code when users clicks on download button?
Can anyone show me code or at least provide some hints on how to do that

Look into Javascript database functions. Javascript isn't my area so the only additional information I can provide would be from google.

Where does download button leads to? If it leads to file like download.php?file_id=xxx, you can easily add a few lines of PHP code to download.php file to count downloads.

I believe Hosting24's proposal would be best, since it doesn't require javascript. Have your link go to download.php with a given id. That page would look up which file it is in a database and serve it via php, by first sending (printing) the correct file headers and then use readfile().

For example, if the current file is an image, you would send a header with mime-type image/jpeg, then call readfile() with the image path. The user's address bar would say something like domain.com/download.php?id=xxx but the browser would display an image, just as if the address were domain.com/image.jpg

This way would also "protect" your files' actual location on the server, since the user only sees a file id, not a location. It makes an additional defense when users can upload files, because people can't upload disguised harmful php files and run them by accessing their location.

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Otherwise you could use AJAX to call a php page with an onclick, which would then incrase the counter. I highly recommend the javascript library jQuery for this. I'm not good with javascript but jQuery was easy evan for me

Just remember, PHP is a pre-processing language. The acronym is a bit nonsensical, but it helps convey the meaning:

PHP = PHP Hypertext Pre-Processor

This means all PHP is done executing by the time anything hits the browser. If you want to then add events or behaviors, you can't, at least not with PHP, since its interpreter has exited. PHP is a server-side language only. If you want something to happen after there is a website viewable in the browser, you need a client-side language.

Originally Posted by lizciz

I believe Hosting24's proposal would be best, since it doesn't require javascript. Have your link go to download.php with a given id. That page would look up which file it is in a database and serve it via php, by first sending (printing) the correct file headers and then use readfile().

For example, if the current file is an image, you would send a header with mime-type image/jpeg, then call readfile() with the image path. The user's address bar would say something like domain.com/download.php?id=xxx but the browser would display an image, just as if the address were domain.com/image.jpg

This way would also "protect" your files' actual location on the server, since the user only sees a file id, not a location. It makes an additional defense when users can upload files, because people can't upload disguised harmful php files and run them by accessing their location.

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Otherwise you could use AJAX to call a php page with an onclick, which would then incrase the counter. I highly recommend the javascript library jQuery for this. I'm not good with javascript but jQuery was easy evan for me

Agreed with this, AJAX can be quite complex to a first time user which I believe you will be if you haven't concidered it yet. jQuery is a very useful resource and there is lots of help if you search through google. If you do wish to keep filesize down though then I'd still recommend googleing the onclick function for javascript as it is only a few lines of code instead of the larger file of jQuery

Thanks a lot to all who helped.
I went with hosting's method and it worked like magic, so thanks a lot hosting's

No problems. Sometimes the best solution is the most simple one