查看数据库数据量大小，占用磁盘大小

本次测试使用 mysql 数据库
数据库名 demo

1. 查看现有数据库

show databases;
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2. 进入information_schema 数据库（存放了其他的数据库的信息）

use information_schema;
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3. 查看 information_schema 数据库表信息

select * from information_schema.tables;
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4. 查询所有数据的总大小：

select concat(round(sum(data_length/1024/1024),2),'MB') as data from information_schema.tables;
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5. 查看实例下所有数据库的空间占用情况，并按从大小排序

select table_schema ,concat(round(sum(data_length/1024/1024),2),'MB') as data from information_schema.tables where table_schema like '%%' group by table_schema order by data desc;
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6.查看指定数据库的大小：

select concat(round(sum(data_length/1024/1024),2),'MB') as data from information_schema.tables where table_schema='demo' ;
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7. 查看指定数据库下的所有表的空间占用情况，并按从大到小排序

select table_name,round(sum(data_length/1024/1024),2) as size from information_schema.tables where table_schema='demo' group by table_name order by size desc;
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8. 查看指定数据库的某个表的大小

select concat(round(sum(data_length/1024/1024),2),'MB') as data from information_schema.tables where table_schema='demo' and table_name='t_student' ;
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其他

select table_schema ,
round(sum(data_length/1024/1024),2) as data_length ,
round(sum(DATA_FREE/1024/1024),2) as data_free ,
round(sum(INDEX_LENGTH/1024/1024),2) as INDEX_LENGTH from information_schema.tables where table_schema='demo' group by table_schema order by data_length;

select
TABLE_SCHEMA
,sum(DATA_LENGTH)/1024/1024/1024 as size_DATA_LENGTH_g
,sum(INDEX_LENGTH)/1024/1024/1024 as size_INDEX_LENGTH_g
,sum(DATA_FREE)/1024/1024/1024 as size_DATA_FREE_g
,sum((DATA_LENGTH+INDEX_LENGTH+DATA_FREE))/1024/1024/1024 as size_g
from information_schema.tables
where table_type = 'BASE TABLE'
group by TABLE_SCHEMA
order by size_DATA_FREE_g
;

select
TABLE_NAME
,sum(DATA_LENGTH)/1024/1024/1024 as size_DATA_LENGTH_g
,sum(INDEX_LENGTH)/1024/1024/1024 as size_INDEX_LENGTH_g
,sum(DATA_FREE)/1024/1024/1024 as size_DATA_FREE_g
,sum((DATA_LENGTH+INDEX_LENGTH+DATA_FREE))/1024/1024/1024 as size_g
from information_schema.tables
where table_type = 'BASE TABLE'
and table_schema = 'db_name'
– and TABLE_NAME = 'table_name'
group by TABLE_NAME
order by size_g desc
limit 20
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