[MySQL] distinct和order by共存对索引选择的影响

SELECT DISTINCT p.products_id, p.sj_id, p.px_id, p.products_model, p.products_p_w_picpath, pd.products_name
FROM products AS p LEFT JOIN products_description AS pd ON pd.products_id=p.products_id
WHERE 1 AND p.products_status=1 ORDER BY p.products_date_added DESC LIMIT 0, 20;

+----+-------------+-------+------+---------------+---------+---------+-----------------------------+-------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key   | key_len | ref             | rows  | Extra                    |
+----+-------------+-------+------+---------------+---------+---------+-----------------------------+-------+----------------------------------------------+
|  1 | SIMPLE    | p   | ALL  | NULL      | NULL  | NULL  | NULL            | 71180 | Using where; Using temporary; Using filesort |
|  1 | SIMPLE    | pd  | ref  | PRIMARY     | PRIMARY | 4     | banggood_work.p.products_id |   1 |                        |
+----+-------------+-------+------+---------------+---------+---------+-----------------------------+-------+----------------------------------------------+

+----+-------------+-------+-------+---------------+---------------------+---------+-----------------------------+------+-------------+
| id | select_type | table | type  | possible_keys | key         | key_len | ref             | rows | Extra     |
+----+-------------+-------+-------+---------------+---------------------+---------+-----------------------------+------+-------------+
|  1 | SIMPLE    | p   | index | NULL      | products_date_added | 8     | NULL            |   20 | Using where |
|  1 | SIMPLE    | pd  | ref   | PRIMARY     | PRIMARY       | 4     | banggood_work.p.products_id |  1 |       |
+----+-------------+-------+-------+---------------+---------------------+---------+-----------------------------+------+-------------+