Hi, The trick is to catch the x,y pixel coords from the user click on the mapserver generated map image, translate them into world coords of the projection you are using (or lat/lon) and then generate a sql and fire that against the database server. This is the approach which the dhtml interface called AppForMap on mapuse.net is using. It uses a small javascript called libs/getClickPosition.js (in the cvs tree) to insure cross browser support for the click. The sql query and all the coord translating stuff are done on the server using php.
There is actually no need for asynchronous HTML voodoo, you could reload the whole page for every click, but in these AJAX times this is not considered cool. So therefore AppForMap also support asynchronous javascript and xml in the next version, which I believed is to be released this weekend. /martin
