如何在 MySQL 数据库管理中，查询数据库、表、索引的容量大小？我们可以在 MySQL 自带的 information_schema 库中的 Table 表里，找到所需信息。

在每个 MySQL 实例中，都有一个独立的 information_schema 库，它是自带的默认库，记录着这个 MySQL 实例中所有数据库的元数据、统计信息、以及有关 MySQL 的访问权限信息。这其中就包括了所有数据库、表、索引的详细信息。

常用 information_schema 库中 Table 表里的字段：

TABLE_SCHEMA : 数据库名
TABLE_NAME：表名
ENGINE：所使用的存储引擎
TABLES_ROWS：记录数
DATA_LENGTH：数据容量大小
INDEX_LENGTH：索引容量大小

有关 information_schema.TABLES 更多字段信息，使用以下命令查看

use information_schema
SHOW COLUMNS FROM TABLES;

更多有关 information_schema 的信息,可查看 MySQL手册

「所有库」的大小

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)',
 sum(truncate(DATA_FREE/1024/1024, 2)) as '碎片占用(MB)'
from 
 information_schema.tables
group by 
 table_schema
order by 
 sum(data_length) desc, sum(index_length) desc;

特别提示：data_length 、index_length 等字段，所存储的容量信息单位是字节，所以我们要除以 2 个 1024 把字节转化为可读性更强的 MB

「指定库」的大小

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)',
 sum(truncate(DATA_FREE/1024/1024, 2)) as '碎片占用(MB)'
from 
 information_schema.tables
where 
 table_schema='WUXI_Monitor'
order by 
 data_length desc, index_length desc;

「指定库」中「所有表」的大小

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)',
  truncate(DATA_FREE/1024/1024, 2) as '碎片占用(MB)'
from 
  information_schema.tables
where 
  table_schema='WUXI_Monitor'
order by 
  data_length desc, index_length desc;

「指定库」中「指定表」的大小

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)',
  truncate(DATA_FREE/1024/1024, 2) as '碎片占用(MB)'
from 
  information_schema.tables
where 
  table_schema='WUXI_Monitor' and table_name='warnrecord'
order by 
  data_length desc, index_length desc;

容量排名前 10 的表

USE information_schema;
SELECT 
  TABLE_SCHEMA as '数据库',
  table_name as '表名',
  table_rows as '记录数',
  ENGINE as '存储引擎',
  truncate(data_length/1024/1024, 2) as '数据容量(MB)',
  truncate(index_length/1024/1024, 2) as '索引容量(MB)',
  truncate(DATA_FREE/1024/1024, 2) as '碎片占用(MB)'
from tables 
order by table_rows desc limit 10;

指定库」中，容量排名前 10 的表

USE information_schema;
SELECT 
  TABLE_SCHEMA as '数据库',
  table_name as '表名',
  table_rows as '记录数',
  ENGINE as '存储引擎',
  truncate(data_length/1024/1024, 2) as '数据容量(MB)',
  truncate(index_length/1024/1024, 2) as '索引容量(MB)',
  truncate(DATA_FREE/1024/1024, 2) as '碎片占用(MB)'
from  tables 
where 
  table_schema='WUXI_Monitor' 
order by table_rows desc limit 10;