mysql数据库计算库空间使用率sql语句

mysql数据库计算库空间的使用率(含有百分比)怎么计算?

select sch.*, sch.data_size/total.total as percentage from
(select TABLE_SCHEMA, truncate(sum(data_length)/1024/1024,2) as data_size,
truncate(sum(index_length)/1024/1024,2) as index_size
from information_schema.tables
group by TABLE_SCHEMA) sch,
(select truncate(sum(data_length)/1024/1024,2) total from information_schema.tables) total