要想知道每个数据库的大小的话，步骤如下：
1、进入information_schema 数据库（存放了其他的数据库的信息）
use information_schema;
2、查询所有数据的大小：
select concat(round(sum(data_length/1024/1024),2),\'MB\') as data from tables;
3、查看指定数据库的大小：
比如查看数据库home的大小
select concat(round(sum(data_length/1024/1024),2),\'MB\') as data from tables where table_schema=\'home\';
4、查看指定数据库的某个表的大小
比如查看数据库home中 members 表的大小
select concat(round(sum(data_length/1024/1024),2),\'MB\') as data from tables where table_schema=\'home\' and table_name=\'members\';
mysql查看当前所有的数据库和索引大小
select table_schema, concat(truncate(sum(data_length)/1024/1024,2),\' mb\') as data_size,
concat(truncate(sum(index_length)/1024/1024,2),\'mb\') as index_size
from information_schema.tables
group by table_schema
order by data_length desc;
mysql查看当前某个数据库和数据库下所有的表的大小
select table_name, concat(truncate(data_length/1024/1024,2),\' mb\') as data_size,
concat(truncate(index_length/1024/1024,2),\' mb\') as index_size
from information_schema.tables where table_schema = \'mysql\'
group by table_name
order by data_length desc;