SELECT `id`,`title`,`thumb` FROM `tp_news` WHERE `status` = 1 AND `hot` = 1 AND `recommend` = 1 LIMIT 20;

这个sql语句
status：状态，值有0,1,-1
hot：是否热门，值有0,1
recommend：是否推荐，值有0,1

下面是这个表的索引

PRIMARY KEY (`id`),
  KEY `status_hot_rec` (`status`,`hot`,`recommend`) USING BTREE

这是建立索引后的sql执行计划

mysql> explain SELECT `id`,`title`,`thumb` FROM `tp_news` WHERE `status` = 1 AND `hot` = 1 AND `recommend` = 1 LIMIT 20;
+----+-------------+-------+------------+------+--------------------+--------------------+---------+-------+------+----------+-----------------------+
| id | select_type | table   | partitions | type | possible_keys  | key            | key_len | ref   | rows | filtered | Extra                 |
+----+-------------+-------+------------+------+--------------------+--------------------+---------+-------+------+----------+-----------------------+
|  1 | SIMPLE      | tp_news | NULL       | ref  | status_hot_rec | status_hot_rec | 1       | const | 8677 |     1.00 | Using index condition |
+----+-------------+-------+------------+------+--------------------+--------------------+---------+-------+------+----------+-----------------------+

这是没有建立索引的sql执行计划

mysql> explain SELECT `id`,`title`,`thumb` FROM `tp_news` WHERE `status` = 1 AND `hot` = 1 AND `recommend` = 1 LIMIT 20;
+----+-------------+-------+------------+------+---------------+------+---------+------+-------+----------+-------------+
| id | select_type | table   | partitions | type | possible_keys | key  | key_len | ref  | rows  | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+------+---------+------+-------+----------+-------------+
|  1 | SIMPLE      | tp_news | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 17354 |     0.10 | Using where |
+----+-------------+-------+------------+------+---------------+------+---------+------+-------+----------+-------------+

对比发现
增加索引后rows 少了差不多50%
但是filtered才只有1，是不是太少了

我这样建立的索引是否合理呢？

请老师指导一二。谢谢！！