MySQL join optimization - bypassing filesort

CREATE TABLE `posts_tags` (
  `id` int(11) NOT NULL auto_increment,
  `post_id` int(11) default NULL,
  `tag_id` int(11) default NULL,
  `post_created_at` datetime default NULL,
  `created_at` datetime default NULL,
  `updated_at` datetime default NULL,
  PRIMARY KEY  (`id`),
  KEY `index_posts_tags_on_post_id_and_tag_id` (`post_id`,`tag_id`)
) ENGINE=InnoDB;

(tag_id, post_created_at)

select * from 
  (
   SELECT count(productID) AS commonProducts, s.productId, s.packageID 
   FROM supply as s
   WHERE EXISTS
   (
      select 1 from supply as innerS 
        where innerS.productID in (2,3,4,5,6,7,8,9,10) 
          and s.productId = innerS.productId 
   )
   GROUP BY s.packageID
  ) AS t
ORDER BY t.commonProducts 
DESC LIMIT 10

SELECT some_fields
FROM (
    SELECT other_fields
    FROM table1, table2
    WHERE join_condition_table1_table2 AND some_other_condition
) AS subquery, table3
WHERE join_condition_subquery_table3
GROUP BY another_field

SELECT some_fields
FROM table1, table2, table3
WHERE
    join_condition_table1_table2
    AND join_condition_subquery_table3 -- actually rewrite this ans a join of either table1 and table3, or table2 and table3
    AND some_other_condition
GROUP BY another_field

SELECT p.date_fact, UNIX_TIMESTAMP(p.date_fact),
       COUNT(DISTINCT p.purchase_id) AS Num
FROM purchase p
WHERE p.date_fact >= '2017-01-01' AND
      p.date_fact <= '2017-01-31' AND
      p.fact_type = 3 AND
      p.purchase_id_primary IS NULL
GROUP BY p.date_fact;