How to execute an ajax sql query

First off, I’m pretty new to wordpress.

I’m trying to build a mini gallery consisting of 4 images that updates to new images every so often. My first attempt was to build a php script that queries the wp-posts table for all attachments with an image post_mime_type, and updates based on the returned data, but I see I can’t run scripts as I normally would. sooo….

I know there’s a smarter way to go around this, but when you have a deadline you have to work with what you know, so if anyone has any better ideas how to go about this, or how to execute a sql query from a javascript ajax call, I would be very grateful.