What to do if the parameter of a function is not defined? (PHP)

I have static function getQuery(isset(开发者_如何学Go$var)?$var:$var="no") which does not work.

I want to use it either by DoDb::getQuery(); or DoDb::getQuery($var); depending on the necessities.

static function getQuery($var="no")

Look at this page http://tuxradar.com/practicalphp/4/15/5. This is the same in many language ;)