How to Show All in Advanced Search

[Apryle Craig]

I am setting up an advanced search form. The user can input data into a form <select> such as selecting a specific Driver Number, Post Color, and Business Name to see all posts from of that type.

What I am unsure of is how to most efficiently make it so they can "view all" of a certain driver number, post color, or business name. They might want to pull all posts that are driver 5, any color, all businesses. Or, all drivers, orange, all businesses.

I currently use:

$result = mysql_query("SELECT * FROM posts WHERE drivernumber='$selecteddriver' && postcolor='$selectedcolor' && businessid='$selectedbusiness' ORDER BY postdate ASC, posttime ASC");

Any help is appreciated.