Make division in post_query?

MySQL can do math but can’t pass it through query_posts like that, or any WordPress’ post query functions, which depend upon WP_Query. They will literally look for a table/column named, in your case, “meta_value_num / date”. To do it in SQL I believe– aka., this is untested– you’d have to do something like this:

SELECT (meta_value_num / DATE()) as ddiv
FROM <some-table>
ORDER BY ddiv

And that isn’t going to be a very efficient query anyway.

Why can’t you do the division after the query? I believe the sort order will be the same either way.