mysql>SELECT name,'yejr',length(name),length('yejr')
mysql>FROM user WHERE name ='yejr';
Empty set (0.00 sec)
mysql>
mysql>
mysql>SELECT name,'yejr',length(name),length('yejr')
mysql>FROM user WHERE uid=1;
+---------+------+--------------+----------------+
| name    | yejr | length(name) | length('yejr') |
+---------+------+--------------+----------------+
| yejr    | yejr | 4            | 4              |
+---------+------+--------------+----------------+
mysql>
mysql>SELECT name,'yejr',length(name),length('yejr')
mysql>FROM user WHERE uid=1 AND name='yejr';
Empty set (0.00 sec)

mysql> CHECK TABLE user;
+---------------------+-------+----------+---------------------------------------------------------+
| Table    | Op    | Msg_type | Msg_text                                                |
+---------------------+-------+----------+---------------------------------------------------------+
| yejr.user | check | error    | Checksum for key:  2 doesn't
match checksum for records |
| yejr.user | check | error    | Corrupt                                                 |
+--------+-------+----------+---------------------------------------------------------+
2 rows in set (0.04 sec)

mysql>REPAIR TABLE user;
+--------+--------+----------+----------+
| Table    | Op     | Msg_type | Msg_text |
+--------+--------+----------+----------+
| yejr.user | repair | status   | OK       |
+--------+--------+----------+----------+

MyISAM 现在使用更好的校验和算法了

总结一下，通常情况下，直接拷贝MyISAM数据文件即可实现低成本升级，但是如果碰到了字符集以及版本变化比较大的时候，最好看看本文以及上述提到的
另外两篇文章。还有就是，如果出现一些异常情况了，就先执行 CHECK TABLE 来看看数据表是否有问题，然后再决定下一步该怎么做。