mysql> use information_schema; 

Database changed

mysql>  select data_length,index_length  

    ->  from tables where 

    ->  table_schema='数据库名' 

    ->  and table_name = '表名'; 

+-------------+--------------+

| data_length | index_length |

+-------------+--------------+

|    3541554 |            0 |

+-------------+--------------+

1 row in set (0.00 sec)

有关information_schema系统数据库的详细信息：http://dev.mysql.com/doc/refman/5.1/zh/information-schema.html