mysql> EXPLAIN SELECT * FROM employee WHERE last = 'Müller';
 +----+-------------+----------+------+---------------+------+---------+------+------+-------------+
 | id | select_type | table    | type | possible_keys | key  | key_len | ref  | rows | Extra       |
 +----+-------------+----------+------+---------------+------+---------+------+------+-------------+
 |  1 | SIMPLE      | employee | ALL  | NULL          | NULL | NULL    | NULL |  987 | Using where |
 +----+-------------+----------+------+---------------+------+---------+------+------+-------------+

 mysql> ALTER TABLE employee ADD INDEX (last);

 mysql> EXPLAIN SELECT * FROM employee WHERE last = 'Müller';
 +----+-------------+----------+------+---------------+------+---------+-------+------+--------------+
 | id | select_type | table    | type | possible_keys | key  | key_len | ref   | rows | Extra        |
 +----+-------------+----------+------+---------------+------+---------+-------+------+--------------+
 |  1 | SIMPLE      | employee | ref  | last          | last | 67      | const |    1 | Using index condition |
 +----+-------------+----------+------+---------------+------+---------+-------+------+--------------+