MySQL区分用户名大小写

以前一直没有注意MySQL中用户名大小写的问题，因为用户名一般都是小写的。今天Ansgar给我设置了一个MySQL账户，用户名为Dingjun。这样我用小写的用户名登陆
jiad4701@urts96:~> mysql -u dingjun -p
Enter password:
ERROR 1045 (28000): Access denied for user 'dingjun'@'localhost' (using password: YES)

就得到错误提示。使用区分大小写的用户名就没有问题：
jiad4701@urts96:~> mysql -u Dingjun -p
Enter password:
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 264184 to server version: 4.1.13
Type 'help;' or '\h' for help. Type '\c' to clear the buffer.