<h3>查询所有[数据库]占用磁盘空间大小</h3>
<pre>
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_size desc;

order by data_length desc;

</pre>

<h3>查询单个库中所有表磁盘占用大小</h3>
<pre>
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;
</pre>

<h3>information_schema 中有数个只读表。它们实际上是视图 ，而不是基本表，因此，你将无法看到与之相关的任何文件</h3>
<pre>
mysql> desc information_schema.tables;
+-----------------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------------+---------------------+------+-----+---------+-------+
| TABLE_CATALOG | varchar(512) | NO | | | |
| TABLE_SCHEMA | varchar(64) | NO | | | | 数据库名
| TABLE_NAME | varchar(64) | NO | | | | 表名
| TABLE_TYPE | varchar(64) | NO | | | | 引擎
| ENGINE | varchar(64) | YES | | NULL | |
| VERSION | bigint(21) unsigned | YES | | NULL | | 是否压缩
| ROW_FORMAT | varchar(10) | YES | | NULL | |
| TABLE_ROWS | bigint(21) unsigned | YES | | NULL | |
| AVG_ROW_LENGTH | bigint(21) unsigned | YES | | NULL | |
| DATA_LENGTH | bigint(21) unsigned | YES | | NULL | | 数据空间大小
| MAX_DATA_LENGTH | bigint(21) unsigned | YES | | NULL | |
| INDEX_LENGTH | bigint(21) unsigned | YES | | NULL | | 数据索引大小
| DATA_FREE | bigint(21) unsigned | YES | | NULL | |
| AUTO_INCREMENT | bigint(21) unsigned | YES | | NULL | |
| CREATE_TIME | datetime | YES | | NULL | |
| UPDATE_TIME | datetime | YES | | NULL | |
| CHECK_TIME | datetime | YES | | NULL | |
| TABLE_COLLATION | varchar(32) | YES | | NULL | |
| CHECKSUM | bigint(21) unsigned | YES | | NULL | |
| CREATE_OPTIONS | varchar(255) | YES | | NULL | |
| TABLE_COMMENT | varchar(2048) | NO | | | |
+-----------------+---------------------+------+-----+---------+-------+
</pre>