use  information_schema

select concat(round(sum(DATA_LENGTH/1024/1024),2),‘M‘),concat(round(sum(INDEX_LENGTH/1024/1024),2),‘M‘) from tables where table_schema=’mytest’ AND table_name=’test’; 

文章来源链接： http://www.cnblogs.com/diandiandidi/p/5582309.html

mysql查询表的数据大小