原理

在mysql中有一个默认的数据表information_schema，information_schema这张数据表保存了MySQL服务器所有数据库的信息。如数据库名，数据库的表，表栏的数据类型与访问权限等。再简单点，这台MySQL服务器上，到底有哪些数据库、各个数据库有哪些表，每张表的字段类型是什么，各个数据库要什么权限才能访问，等等信息都保存在information_schema表里面，所以请勿删改此表。

注意：使用查询命令前先切换到数据表

use information_schema;

查询样例的库：short_video 表：video_info

查看所有数据库容量大小

select
 table_schema as '数据库',
 sum(table_rows) as '记录数',
 sum(truncate(data_length/1024/1024, 2)) as '数据容量(MB)',
 sum(truncate(index_length/1024/1024, 2)) as '索引容量(MB)'
from 
 information_schema.tables
group by 
 table_schema
order by 
 sum(data_length) desc, 
 sum(index_length) desc;

查看指定数据库使用大小

select concat(round(sum(data_length/1024/1024),2),'MB') as data from tables where table_schema='short_video';

查看表使用大小

select concat(round(sum(data_length/1024/1024),2),'MB') as data from tables where table_schema='short_video' and 
table_name='video_info';

查看所有数据库容量大小

select
table_schema as '数据库',
sum(table_rows) as '记录数',
sum(truncate(data_length/1024/1024, 2)) as '数据容量(MB)',
sum(truncate(index_length/1024/1024, 2)) as '索引容量(MB)'
from information_schema.tables
group by table_schema
order by sum(data_length) desc, sum(index_length) desc;

查看所有数据库各表容量大小

select
table_schema as '数据库',
table_name as '表名',
table_rows as '记录数',
truncate(data_length/1024/1024, 2) as '数据容量(MB)',
truncate(index_length/1024/1024, 2) as '索引容量(MB)'
from information_schema.tables
order by data_length desc, index_length desc;

查看指定数据库容量大小

select
table_schema as '数据库',
sum(table_rows) as '记录数',
sum(truncate(data_length/1024/1024, 2)) as '数据容量(MB)',
sum(truncate(index_length/1024/1024, 2)) as '索引容量(MB)'
from information_schema.tables
where table_schema='short_video';

查看指定数据库各表容量大小

select
  table_schema as '数据库',
  table_name as '表名',
  table_rows as '记录数',
  truncate(data_length/1024/1024, 2) as '数据容量(MB)',
  truncate(index_length/1024/1024, 2) as '索引容量(MB)'
from information_schema.tables
where table_schema='short_video'
order by data_length desc, index_length desc;