OK, I guess I'm not clear on what was wrong when you had the second criteria set to AND.
if when using and for both, it should ignore the criteria if you leave it empty. It should only e part of the search if you enter a value.
as for the google search, a well designed web site will have a keywords meta tag for each page. The web site developer will add a keywords list to this meta tag that should return the page. So in the case of searching for cameras the keywords meta tag would contain both cameras and camera:
<meta name="keywords" content="cameras, camera">
you could create a similar column in your database and use that column in the search rather than the item name column.