Query Pages Where Custom Field Exists

This search,
https://www.google.com/search?q=wordpress+custom+fields+excerpt

found, among others, this:
https://www.flisterz.com/2008/06/07/wordpress-conditional-statement-using-custom-fields/

meta_key and meta_value are valid query parameters for the WP_Query object in 2.6.2.

To get all the pages for a given meta key, one could do something like this:
$myquery = WP_Query('post_type=page&meta_key=MYKEY');

Thanks so much!

hi from Italy
how can i wp-query posts for a certain category and order by a certain metakey? eg. surname alphabetically?