PostgreSQL中将对象oid和对象名相互转换

PostgreSQL中将对象oid转为对象名

使用pg的内部数据类型将对象oid转为对象名，可以简化一些系统视图的关联查询。

数据库类型转换对应类型的oid

可以用以下数据库类型转换对应类型的oid（以pg12为例）

postgres=# select typname from pg_type where typname ~ '^reg';
    typname
---------------
 regclass
 regconfig
 regdictionary
 regnamespace
 regoper
 regoperator
 regproc
 regprocedure
 regrole
 regtype
(10 rows)

对应关系

对象名称	类型	转换规则
pg_class	regclass	pg_class.oid::regclass
pg_ts_dict	regdictionary	pg_ts_dict.oid::regdictionary
pg_namespace	regnamespace	pg_namespace.oid::regnamespace
pg_operator	regoperator	pg_operator.oid::regoperator
pg_proc	regproc	pg_proc.oid::regproc
pg_roles pg_user	regrole	pg_roles.oid::regrole pg_user.usesysid::regrole
pg_type	regtype	pg_type.oid::regtype
	以下几个类型暂不确定用途，待研究：
	regprocedure
	regoper
	regconfig

创建测试数据

psql -U postgres
create user test password 'test';
create database testdb with owner=test;
\c testdb
CREATE SCHEMA AUTHORIZATION test;
psql -U test -d testdb
create table test_t1(id int);
create table test_t2(id int);
create table test_t3(id int);

基于如上测试数据，查询test模式下有哪些表，以及表的owner

传统表关联的方式使用以下SQL，关联pg_class、pg_namespace、pg_roles/pg_user

psql -U test -d testdb
-- 查询用户关联pg_user查询
SELECT
  t3.nspname AS SCHEMA,
  t1.relname AS tablename,
  t2.usename AS OWNER
FROM
  pg_class t1
  JOIN pg_user t2 ON t1.relowner = t2.usesysid
  JOIN pg_namespace t3 ON t1.relnamespace = t3.OID
WHERE
  t1.relkind = 'r'
  AND t3.nspname = 'test';

 schema | tablename | owner
--------+-----------+-------
 test   | test_t1   | test
 test   | test_t2   | test
 test   | test_t3   | test
(3 rows)

-- 查询用户关联pg_roles查询
SELECT
  t3.nspname AS SCHEMA,
  t1.relname AS tablename,
  t2.rolname AS OWNER
FROM
  pg_class t1
  JOIN pg_roles t2 ON t1.relowner = t2.oid
  JOIN pg_namespace t3 ON t1.relnamespace = t3.OID
WHERE
  t1.relkind = 'r'
  AND t3.nspname = 'test';

 schema | tablename | owner
--------+-----------+-------
 test   | test_t1   | test
 test   | test_t2   | test
 test   | test_t3   | test
(3 rows)

如上为了实现查询效果需要关联三张表，查询比较繁琐，如果使用对象转换就很简单了，如下：

psql -U test -d testdb
SELECT
  relnamespace :: REGNAMESPACE AS SCHEMA,
  relname AS tablename,
  relowner :: REGROLE AS OWNER
FROM
  pg_class
WHERE
  relnamespace :: REGNAMESPACE :: TEXT = 'test'
  AND relkind = 'r';

 schema | tablename | owner
--------+-----------+-------
 test   | test_t1   | test
 test   | test_t2   | test
 test   | test_t3   | test
(3 rows)

将对象名转为oid类型

转换关系

对象类型	转换规则
table	'表名'::regclass::oid
function/procedure	'函数名/存储过程名'::regproc::oid
schema	'模式名'::regnamespace::oid
user/role	'用户名/角色名'::regrole::oid
type	'类型名称'::regtype::oid

测试示例

表转换

drop table if exists test_t;
create table test_t(id int);

postgres=# select oid from pg_class where relname = 'test_t';
  oid
-------
 16508
(1 row)

postgres=# select 'test_t'::regclass::oid;
  oid
-------
 16508
(1 row)

函数转换

CREATE OR REPLACE FUNCTION test_fun(
    arg1 INTEGER,
    arg2 INTEGER,
    arg3 TEXT
)
RETURNS INTEGER
AS $$
BEGIN
    RETURN arg1 + arg2;
END;
$$ LANGUAGE plpgsql;

postgres=# select oid,proname from pg_proc where proname = 'test_fun';
  oid  | proname
-------+----------
 16399 | test_fun
(1 row)

postgres=# select 'test_fun'::regproc::oid;
  oid
-------
 16399
(1 row)

模式转换

create schema test_schema;

postgres=# select oid,nspname from pg_namespace where nspname='test_schema';
  oid  |   nspname
-------+-------------
 16511 | test_schema
(1 row)

postgres=# select 'test_schema'::regnamespace::oid;
  oid
-------
 16511
(1 row)

用户/角色

create user test_user;

postgres=# select usesysid,usename from pg_user where usename='test_user';
 usesysid |  usename
----------+-----------
    16512 | test_user
(1 row)

postgres=# select 'test_user'::regrole::oid;
  oid
-------
 16512
(1 row)

类型

CREATE TYPE type_sex AS ENUM ('male', 'female');

postgres=# select oid,typname from pg_type where typname='type_sex';
  oid  | typname
-------+----------
 16514 | type_sex
(1 row)

postgres=# select 'type_sex'::regtype::oid;
  oid
-------
 16514
(1 row)