无论如何，您都可以知道：

mysql> select @@datadir;
+----------------------------------------------------------------+
| @@datadir                                                      |
+----------------------------------------------------------------+
| D:\Documents and Settings\b394382\My Documents\MySQL_5_1\data\ |
+----------------------------------------------------------------+
1 row in set (0.00 sec)

感谢MySql论坛的Barry Galbraith
http://forums.mysql.com/read.php?10,379153,379167#msg-379167