-- explain2.txt

EXPLAIN
 SELECT * FROM person
  WHERE id = '9996';

+----+-------------+--------+-------+---------------+---------+---------+-------+------+-------+
| id | select_type | table  | type  | possible_keys | key     | key_len | ref   | rows | Extra |
+----+-------------+--------+-------+---------------+---------+---------+-------+------+-------+
|  1 | SIMPLE      | person | const | PRIMARY       | PRIMARY | 5       | const |    1 |       |
+----+-------------+--------+-------+---------------+---------+---------+-------+------+-------+

MySQL uses the PRIMARY key, finding out which row has the id of '9996', and then 
going directly to that row.