mysql ORDER BY two different fields

This basically select posts from the database (post_id is the id of the post its selecting) and ordering this by the number of rows with this post id in it.

How can I order this by amount of posts with this id (as currently), AND by date, newest ones first but in the order of number of them in the database.

mysql_query("SELECT post_id, COUNT(post_id) FROM postvoting GROUP BY post_id ORDER BY COUNT(post_id) DESC ");

ORDER BY one_thing, another_thing

oh, i forgot, I need to order it by the date of the Post_id row in a different table of the same database. I want to order it by the number of rows of the same post_id in the postvoting table, and then order it by the date field in the posts table where the id of the row is equal to post_id in postvoting.

You're querying FROM the second table too.

Add the ORDER BY as given above.

Add a WHERE x.id_1=y.id_2 (x and y are the table names, id_1 and id_2 are the field names)