mysql执行计划key_len长度

Question

求教key_len是4是怎么算的，数据库编码为utf8mysql> desc t1;
+-------------+-------------+------+-----+---------+----------------+
| Field       | Type        | Null | Key | Default | Extra          |
+-------------+-------------+------+-----+---------+----------------+
| id          | int(11)     | NO   | PRI | NULL    | auto_increment |
| assist_id   | int(11)     | NO   |     | NULL    |                |
| assist_name | varchar(50) | YES  |     | NULL    |                |
+-------------+-------------+------+-----+---------+----------------+mysql> explain
    -> select * from t1 where id > 1 and id < 5;
+----+-------------+-----------------------+-------+---------------+---------+---------+------+------+-------------+
| id | select_type | table                 | type  | possible_keys | key     | key_len | ref  | rows | Extra       |
+----+-------------+-----------------------+-------+---------------+---------+---------+------+------+-------------+
|  1 | SIMPLE      | t1                    | range | PRIMARY       | PRIMARY | 4       | NULL |    1 | Using where |
+----+-------------+-----------------------+-------+---------------+---------+---------+------+------+-------------+
1 row in set (0.00 sec)

Answer 1

id 是int的型的.....

Answer 2

另外，所索引类型为date和datetime，key_len是怎么计算的？

Answer 3

mysql explain 中key_len的计算http://hidba.org/?p=404

Answer 4

http://blog.csdn.net/mchdba/article/details/9190771

Answer 5

请查看 http://blog.csdn.net/mchdba/article/details/9190771

Answer 6

你的PRIMARY 是 id          | int(11)     | NO   | PRI | NULL    | auto_increment |
INT数据类型，而INT是4字节。或者楼主描述一下自己是如何理解的。