嗨，我是MySQL World的新手。
当我了解MySQL范围优化时，有人提出了与多部分索引有关的问题。
（http://jorgenloland.blogspot.com/2011/08/mysql-range-access-method-explained.html）
问题1： 单间隔和连续间隔是什么意思？
问题2： 与分段索引和键相关
表结构 创建表订单（customer_id int，value int，name varchar（20），primary key（customer_id，value））;
A）
mysql> explain select * from orders where customer_id <= 2 and value = 1;
+----+-------------+--------+------------+-------+---------------+---------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+--------+------------+-------+---------------+---------+---------+------+------+----------+-------------+
| 1 | SIMPLE | orders | NULL | range | PRIMARY | PRIMARY | 8 | NULL | 4 | 25.00 | Using where |
+----+-------------+--------+------------+-------+---------------+---------+---------+------+------+----------+-------------+
B）
mysql> explain select * from orders where customer_id < 2 and value = 1;
+----+-------------+--------+------------+-------+---------------+---------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+--------+------------+-------+---------------+---------+---------+------+------+----------+-------------+
| 1 | SIMPLE | orders | NULL | range | PRIMARY | PRIMARY | 4 | NULL | 4 | 25.00 | Using where |
+----+-------------+--------+------------+-------+---------------+---------+---------+------+------+----------+-------------+
为什么说明语句（A）将keylen显示为 8 ，而（B）将keylen显示为 4