MySQL查询顺序由多个项目

可以按多行订购吗？

我希望我的用户按last_activity进行排序，但同时，我希望带有图片的用户出现在没有图片的用户之前

像这样：

SELECT some_cols
FROM `prefix_users`
WHERE (some conditions)
ORDER BY last_activity, pic_set DESC;

SELECT some_cols
FROM prefix_users
WHERE (some conditions)
ORDER BY pic_set DESC, last_activity;

按图片排序，然后按活动排序：

SELECT some_cols
FROM `prefix_users`
WHERE (some conditions)
ORDER BY pic_set, last_activity DESC;

SELECT id, user_id, video_name
FROM sa_created_videos
ORDER BY LENGTH(id) ASC, LENGTH(user_id) DESC