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_classregclasspg_class.oid::regclasspg_ts_dictregdictionarypg_ts_dict.oid::regdictionarypg_namespaceregnamespacepg_namespace.oid::regnamespacepg_operatorregoperatorpg_operator.oid::regoperatorpg_procregprocpg_proc.oid::regprocpg_roles
pg_userregrolepg_roles.oid::regrole
pg_user.usesysid::regrolepg_typeregtypepg_type.oid::regtype以下几个类型暂不确定用途，待研究：regprocedureregoperregconfig创建测试数据
psql -U postgrescreate user test password 'test';create database testdb with owner=test;\c testdbCREATE SCHEMA AUTHORIZATION test;psql -U test -d testdbcreate 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SELECTt3.nspname AS SCHEMA,t1.relname AS tablename,t2.usename AS OWNER FROMpg_class t1JOIN pg_user t2 ON t1.relowner = t2.usesysidJOIN pg_namespace t3 ON t1.relnamespace = t3.OID WHEREt1.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SELECTt3.nspname AS SCHEMA,t1.relname AS tablename,t2.rolname AS OWNER FROMpg_class t1JOIN pg_roles t2 ON t1.relowner = t2.oidJOIN pg_namespace t3 ON t1.relnamespace = t3.OID WHEREt1.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 testdbSELECTrelnamespace :: REGNAMESPACE AS SCHEMA,relname AS tablename,relowner :: REGROLE AS OWNER FROMpg_class WHERErelnamespace :: 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::oidfunction/procedure'函数名/存储过程名'::regproc::oidschema'模式名'::regnamespace::oiduser/role'用户名/角色名'::regrole::oidtype'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 INTEGERAS $$BEGIN RETURN arg1 + arg2;END;$$ 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)
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