syntax question

couple of questions... I'm am learning php & mysql without any books (will also be using postgres, and informix, but assuming most of these are about the same other then sql syntax), and through internet resources. there are a lot of good step throughs on a lot of stuff, but there are some things I'm having a hard time finding how to's on... for instance - if there a command that will give me the name of the fields in the result set? how to I test for a null value? how do I go from one row to the next, or how do I filter a result set based on a value in a column? is there a way to sum a specific field? would appreciate whatever help I can get, and even better if somebody know's a step through that goes through all the basic's of database syntaxes in php. -- Thanks, Jeff Bluemel