Question

我试图弄清楚如何确定数据库中特定列的大小，例如我有两个名为sourceip，destinationip的列，它们都是16字节字段。

我认为这将在information_schema或\ d +中的某处，但我找不到一个特定的命令来隔离每个列类型的大小。

您可以在数据库中计算列类型大小，还是只需要在Postgresql文档中引用每种类型的字节大小？

Answer 1

pg中只有少数类型具有固定长度 - 几乎所有类型都是varlena类型 - 它具有动态长度。您可以查看

等查询

 postgres=# select typlen from pg_type where oid = 'int'::regtype::oid;
  typlen 
 --------
       4
 (1 row)


 postgres=# select attlen from pg_attribute where attrelid = 'x'::regclass and attname = 'a';
  attlen 
 --------
       4
 (1 row)

当结果不是-1时，则类型没有固定长度

对于varlena类型的

使用pg_column_size函数：

postgres=# \df *size*
                                   List of functions
   Schema   |          Name          | Result data type | Argument data types |  Type  
------------+------------------------+------------------+---------------------+--------
 pg_catalog | pg_column_size         | integer          | "any"               | normal
 pg_catalog | pg_database_size       | bigint           | name                | normal
 pg_catalog | pg_database_size       | bigint           | oid                 | normal
 pg_catalog | pg_indexes_size        | bigint           | regclass            | normal
 pg_catalog | pg_relation_size       | bigint           | regclass            | normal
 pg_catalog | pg_relation_size       | bigint           | regclass, text      | normal
 pg_catalog | pg_size_pretty         | text             | bigint              | normal
 pg_catalog | pg_size_pretty         | text             | numeric             | normal
 pg_catalog | pg_table_size          | bigint           | regclass            | normal
 pg_catalog | pg_tablespace_size     | bigint           | name                | normal
 pg_catalog | pg_tablespace_size     | bigint           | oid                 | normal
 pg_catalog | pg_total_relation_size | bigint           | regclass            | normal
(12 rows)



 postgres=# select pg_column_size('Hello');
  pg_column_size 
 ----------------
          6
 (1 row)

 postgres=# select pg_column_size(10);
  pg_column_size 
 ----------------
               4
 (1 row)

 postgres=# select pg_column_size(now());
  pg_column_size 
 ----------------
               8

在Postgresql中计算列类型的大小

1 个答案: