I wouldn’t say it’s “easy”, but any complex queries like the one you have that can’t be handled via the API, WP_Query
, or its filters should use the wpdb class.
global $wpdb;
$rows = $wpdb->get_results(
"
SELECT p1.meta_value as avg,
p2.meta_value as total,
p1.meta_value * p2.meta_value as product
FROM $wpdb->postmeta as p1,
$wpdb->postmeta as p2
WHERE p1.meta_key = 'crfp-average-rating'
AND p2.meta_key = 'crfp-total-ratings'
AND p1.post_id = p2.post_id
"
);
foreach( $rows as $row ){
print_r( $row );
}