mysql> explain SELECT * FROM wp_comments /*!40000 IGNORE INDEX (comment_approved) */ WHERE comment_post_ID = '1' AND comment_approved = '1' ORDER BY comment_date DESC;
+----+-------------+-------------+------+------------------------+--------+---------+-------------+------+-------------+
| id | select_type | table       | type | possible_keys          | key    | key_len | ref         | rows | Extra       |
+----+-------------+-------------+------+------------------------+--------+---------+-------------+------+-------------+
| 1  | SIMPLE      | wp_comments | ref  | comment_post_ID,comidx | comidx | 5       | const,const | 9    | Using where |
+----+-------------+-------------+------+------------------------+--------+---------+-------------+------+-------------+
1 row in set (0.00 sec)