Uncaught TypeError: Cannot read property 'results' of undefined with YQL json

I'm trying to do YQL with: select * from yahoo.finance.quotes where symbol = "YHOO"

When I do jscript (which I'm using this code - http://james.padolsey.com/javascript/using-yql-with-jsonp/) his query works perfectly, but when I try mine replacing with below.

// Define your callback:
var callback = function(data) {
    var post = data.query.results.quote;
    alert(post.symbol);
};

I always get this error. Is there something I'm missing?

Uncaught TypeError: Cannot read property 'results' of undefined