如何查询数据库中每个表的大小

查询数据库中每个表的大小可以通过不同的数据库管理系统（DBMS）来实现。以下是一些常见数据库系统中查询表大小的常用方法：

MySQL

```sql

SELECT table_schema, table_name, round(((data_length + index_length) / 1024 / 1024), 2) AS `Size (MB)`

FROM information_schema.TABLES

WHERE table_schema NOT IN ('information_schema', 'mysql', 'performance_schema', 'sys')

ORDER BY `Size (MB)` DESC;

```

PostgreSQL

```sql

SELECT

nspname AS "schema",

relname AS "table",

pg_size_pretty(pg_total_relation_size(C.oid)) AS "total_size"

FROM

pg_catalog.pg_class C

LEFT JOIN

pg_catalog.pg_namespace N ON N.oid = C.relnamespace

WHERE

nspname NOT IN ('pg_catalog', 'information_schema')

AND C.relkind <> 'i'

AND c.relname !~ 'pg_'

ORDER BY

pg_total_relation_size(C.oid) DESC;

```

SQL Server

```sql

SELECT

SCHEMA_NAME(t.schema_id) AS SchemaName,

t.name AS TableName,

SUM(a.total_pages) 8 AS TotalSpaceKB

FROM

sys.tables t

INNER JOIN

sys.indexes i ON t.object_id = i.object_id

INNER JOIN

sys.partitions p ON i.object_id = p.object_id AND i.index_id = p.index_id

INNER JOIN

sys.allocation_units a ON p.partition_id = a.container_id

WHERE

t.type = 'U'

GROUP BY

t.schema_id, t.name

ORDER BY

SUM(a.total_pages) 8 DESC;

```

Oracle

```sql

SELECT

table_name,

round(sum(bytes)/1024/1024, 2) as "Size MB"

FROM

user_tables

GROUP BY

table_name

ORDER BY

"Size MB" DESC;

```

请注意，以上SQL查询仅适用于特定数据库的版本，并且可能需要根据你的数据库版本和配置进行调整。在执行这些查询之前，请确保你有足够的权限来访问`information_schema`或`sys`等系统表，因为这些表包含了数据库的元数据信息。