加索引的怪异问题

加索引的怪异问题：数据库的版本是5.5.20
                  linux的版本是CentOS release 6.2 (Final)

添加username和email的索引
(system@localhost) [baike]> create index idx_username on bk_user(username(20));
Query OK, 0 rows affected (0.39 sec)
Records: 0  Duplicates: 0  Warnings: 0

(system@localhost) [baike]> create index idx_email on bk_user(email(30));
Query OK, 0 rows affected (0.44 sec)
Records: 0  Duplicates: 0  Warnings: 0

(system@localhost) [baike]> show index from bk_user;
+---------+------------+--------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table   | Non_unique | Key_name     | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+---------+------------+--------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| bk_user |          0 | PRIMARY      |            1 | uid         | A         |       79429 |     NULL | NULL   |      | BTREE      |         |               |
| bk_user |          1 | loginstatus  |            1 | loginstatus | A         |           3 |     NULL | NULL   |      | BTREE      |         |               |
| bk_user |          1 | idx_username |            1 | username    | A         |         156 |       20 | NULL   | YES  | BTREE      |         |               |
| bk_user |          1 | idx_email    |            1 | email       | A         |         156 |       30 | NULL   | YES  | BTREE      |         |               |
+---------+------------+--------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
4 rows in set (0.01 sec)

(system@localhost) [baike]> desc bk_user;
+----------------+------------------+------+-----+---------+-------+
| Field          | Type             | Null | Key | Default | Extra |
+----------------+------------------+------+-----+---------+-------+
| uid            | bigint(20)       | NO   | PRI | NULL    |       |
| useriden       | char(17)         | YES  |     | NULL    |       |
| username       | char(64)         | YES  | MUL | NULL    |       |
| regdate        | int(10)          | YES  |     | NULL    |       |
| password       | char(32)         | YES  |     | NULL    |       |
| email          | char(255)        | YES  | MUL | NULL    |       |
| status         | tinyint(1)       | YES  |     | NULL    |       |
| image          | char(255)        | YES  |     | NULL    |       |
| bigimage       | varchar(255)     | NO   |     | NULL    |       |
| regip          | char(15)         | YES  |     | NULL    |       |
| lastvisit      | int(10)          | YES  |     | NULL    |       |
| lastip         | char(15)         | YES  |     | NULL    |       |
| loginstatus    | tinyint(1)       | NO   | MUL | 0       |       |
| cas_ticket     | varchar(255)     | NO   |     | NULL    |       |
| is_super_admin | tinyint(1)       | NO   |     | 0       |       |
| type           | tinyint(1)       | NO   |     | 1       |       |
| remark         | varchar(255)     | YES  |     | NULL    |       |
| remark_time    | int(11) unsigned | NO   |     | 0       |       |
+----------------+------------------+------+-----+---------+-------+
18 rows in set (0.00 sec)


(system@localhost) [baike]> set names gbk;
Query OK, 0 rows affected (0.00 sec)

根据userid查得到
(system@localhost) [baike]> select * from bk_user where uid='300001338703';
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
| uid          | useriden          | username | regdate    | password                         | email             | status | image                                                               | bigimage                                                             | regip         | lastvisit  | lastip        | loginstatus | cas_ticket                        | is_super_admin | type | remark | remark_time |
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
| 300001338703 | icVpAUWBwBmZCU0Zx | xxx       | 1313054564 | e1ff996065fda37fa5b5813c3ae726be | xxx@qq.com |      1 | xx.jpg | xx.jpg | xx | 1342143395 | 124.42.60.110 |           1 | ST-12619-JAaU2hsW7JdhG5YHcBEW-sso |              1 |    4 | NULL   |           0 |
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
1 row in set (0.00 sec)

根据username和email查询都是空记录
(system@localhost) [baike]> select * From bk_user where username='xxx';
Empty set (0.00 sec)

(system@localhost) [baike]> select * from bk_user where email='xxx@qq.com';
Empty set (0.00 sec)

修改类型为varchar后，数据即可找到
(system@localhost) [baike]> alter table bk_user modify username varchar(64);
Query OK, 86030 rows affected (5.31 sec)
Records: 86030  Duplicates: 0  Warnings: 0

(system@localhost) [baike]> alter table bk_user modify email varchar(255);
Query OK, 86030 rows affected (4.86 sec)
Records: 86030  Duplicates: 0  Warnings: 0

(system@localhost) [baike]> select * From bk_user where username='xxx';
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
| uid          | useriden          | username | regdate    | password                         | email             | status | image                                                               | bigimage                                                             | regip         | lastvisit  | lastip        | loginstatus | cas_ticket                        | is_super_admin | type | remark | remark_time |
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
| 300001338703 | icVpAUWBwBmZCU0Zx | 刘伽伽       | 1313054564 | e1ff996065fda37fa5b5813c3ae726be | 5549125512@qq.com |      1 | xx/85/46/11300001337475131305460345051_50.jpg | xx/85/46/11300001337475131305460345051_180.jpg | 124.42.60.110 | 1342143395 | 124.42.60.110 |           1 | ST-12619-JAaU2hsW7JdhG5YHcBEW-sso |              1 |    4 | NULL   |           0 |
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
1 row in set (0.02 sec)

(system@localhost) [baike]> select * from bk_user where email='xxx@qq.com';
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
| uid          | useriden          | username | regdate    | password                         | email             | status | image                                                               | bigimage                                                             | regip         | lastvisit  | lastip        | loginstatus | cas_ticket                        | is_super_admin | type | remark | remark_time |
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
| 300001338703 | icVpAUWBwBmZCU0Zx | xxx       | 1313054564 | e1ff996065fda37fa5b5813c3ae726be | 5549125512@qq.com |      1 | xx/85/46/11300001337475131305460345051_50.jpg | xx/85/46/11300001337475131305460345051_180.jpg | 124.42.60.110 | 1342143395 | 124.42.60.110 |           1 | ST-12619-JAaU2hsW7JdhG5YHcBEW-sso |              1 |    4 | NULL   |           0 |
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
1 row in set (0.00 sec)

在修改回来为原来的char类型
(system@localhost) [baike]> alter table bk_user modify username char(64);
Query OK, 86030 rows affected (4.99 sec)
Records: 86030  Duplicates: 0  Warnings: 0

(system@localhost) [baike]> alter table bk_user modify email char(255);
Query OK, 86030 rows affected (5.96 sec)
Records: 86030  Duplicates: 0  Warnings: 0

(system@localhost) [baike]> select * From bk_user where username='xxx';
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
| uid          | useriden          | username | regdate    | password                         | email             | status | image                                                               | bigimage                                                             | regip         | lastvisit  | lastip        | loginstatus | cas_ticket                        | is_super_admin | type | remark | remark_time |
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
| 300001338703 | icVpAUWBwBmZCU0Zx | xxx       | 1313054564 | e1ff996065fda37fa5b5813c3ae726be | 5549125512@qq.com |      1 | xx/85/46/11300001337475131305460345051_50.jpg | xx/85/46/11300001337475131305460345051_180.jpg | 124.42.60.110 | 1342143395 | 124.42.60.110 |           1 | ST-12619-JAaU2hsW7JdhG5YHcBEW-sso |              1 |    4 | NULL   |           0 |
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
1 row in set (0.00 sec)

(system@localhost) [baike]> select * from bk_user where email='xxx@qq.com';
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
| uid          | useriden          | username | regdate    | password                         | email             | status | image                                                               | bigimage                                                             | regip         | lastvisit  | lastip        | loginstatus | cas_ticket                        | is_super_admin | type | remark | remark_time |
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
| 300001338703 | icVpAUWBwBmZCU0Zx | xxx      | 1313054564 | e1ff996065fda37fa5b5813c3ae726be | xxx@qq.com |      1 | xx/85/46/11300001337475131305460345051_50.jpg | xx/85/46/11300001337475131305460345051_180.jpg | 124.42.60.110 | 1342143395 | 124.42.60.110 |           1 | ST-12619-JAaU2hsW7JdhG5YHcBEW-sso |              1 |    4 | NULL   |           0 |
+--------------+-------------------+----------+------------+----------------------------------+-------------------+--------+---------------------------------------------------------------------+----------------------------------------------------------------------+---------------+------------+---------------+-------------+-----------------------------------+----------------+------+--------+-------------+
1 row in set (0.00 sec)

虽然问题可以解决，但是出现的问题很诡异，为什么对一个char类型加上索引，会出现如此的问题，太有意思了，希望有官方给与帮助啊。