我试图弄清楚如何确定数据库中特定列的大小，例如，我有两列称为sourceip，destinationip的列，它们都是16字节字段。
我以为这将是在information_schema或\ d +中的某个位置，但是我找不到用于隔离每种列类型的大小的特定命令。
您可以在数据库中计算列类型的大小，还是只需要在Postgresql文档中引用每种类型的字节大小？
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。您可以检查类似的查询
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，类型没有固定长度
对于varlena类型，请使用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
