SELECT a. * , b.comment_post_id, count( * ) AS fc
FROM evo_posts a
INNER JOIN evo_comments b ON a.ID = b.comment_post_id
GROUP BY b.comment_post_id
ORDER BY fc DESC , post_issue_date DESC

谢谢haitao和pcplayer的帮助。
特别鸣谢haitao兄，我是源于你的思路才做出来的。