在实际的生产环境 ，我们经常会碰到这样的情况：因为业务场景需要，本部门某些重要的业务数据表需要给予其他部门查看权限，因业务的扩展及调整，后期可能需要放开更多的表查询权限。为解决此种业务需求，我们可以采用创建视图的方式来解决，已可以通过创建影子用户的方式来满足需求，本文主要介绍影子用户的创建及授权方法。
session 1:
--创建readonly用户，并将test模式赋予readonly用户。
postgres=# create user readonly with password 'postgres'; CREATE ROLE postgres=# grant usage on schema test to readonly; GRANT postgres=# \dn List of schemas Name | Owner -------+------- test | postgres
session 2:
--登陆readonly用户可以查询test模式下现存的所有表。
postgres=# \c postgres readonly You are now connected to database "postgres" as user "readonly". postgres=> select * from test.emp ; empno | ename | job | mgr | hiredate | sal | comm | deptno -------+--------+-----------+------+------------+---------+---------+-------- 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | | 20 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | | 30 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | | 10 7839 | KING | PRESIDENT | | 1981-11-17 | 5000.00 | | 10 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | | 30 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | | 20 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | | 10 7788 | test | ANALYST | 7566 | 1982-12-09 | 3000.00 | | 20 7876 | ADAMS | CLERK | 7788 | 1983-01-12 | 1100.00 | | 20 1111 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | | 20 (14 rows)
换到session 1创建新表t1
postgres=# create table test.t1 as select * from test.emp; CREATE TABLE
切换到session 2 readonly用户下，t1表无法查询
postgres=> select * from test.t1 ; 2021-03-02 15:25:33.290 CST [21059] ERROR: permission denied for table t1 2021-03-02 15:25:33.290 CST [21059] STATEMENT: select * from test.t1 ; **ERROR: permission denied for table t1
结论：如果只授予 usage on schema 权限，readonly 只能查看 test 模式下已经存在的表和对象。在授予 usage on schema 权限之后创建的新表无法查看。
针对上个场景session 2 **ERROR: permission denied for table t1 错误的处理
postgres=> select * from test.t1 ; **ERROR: permission denied for table t1
session 1： 使用postgres用户授予readonly用户 select on all tables 权限
postgres=# grant select on all tables in schema test TO readonly ;
session 2: readonly用户查询 t1 表
postgres=> select * from test.t1; empno | ename | job | mgr | hiredate | sal | comm | deptno -------+--------+-----------+------+------------+---------+---------+-------- 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | | 20 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | | 30 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | | 10 7839 | KING | PRESIDENT | | 1981-11-17 | 5000.00 | | 10 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | | 30 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | | 20 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | | 10 7788 | test | ANALYST | 7566 | 1982-12-09 | 3000.00 | | 20 7876 | ADAMS | CLERK | 7788 | 1983-01-12 | 1100.00 | | 20 1111 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | | 20 (14 rows)
session1 ：postgres用户的test模式下创建新表 t2
postgres=# create table test.t2 as select * from test.emp; SELECT 14
session 2：readonly用户查询 t2 表权限不足
postgres=> select * from test.t2 ; ERROR: permission denied for table t2
session 1：再次赋予 grant select on all tables
postgres=# grant select on all tables in schema test TO readonly ;
session 2：readonly用户又可以查看 T2 表
postgres=> select * from test.t2 ; empno | ename | job | mgr | hiredate | sal | comm | deptno -------+--------+-----------+------+------------+---------+---------+-------- 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | | 20 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | | 30 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | | 10 7839 | KING | PRESIDENT | | 1981-11-17 | 5000.00 | | 10 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | | 30 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | | 20 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | | 10 7788 | test | ANALYST | 7566 | 1982-12-09 | 3000.00 | | 20 7876 | ADAMS | CLERK | 7788 | 1983-01-12 | 1100.00 | | 20 1111 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | | 20 (14 rows)
如果想让readonly只读用户不在每次 postgres用户在test模式中创建新表后都要手工赋予 grant select on all tables in schema test TO readonly 权限。则需要授予对test默认的访问权限，对于test模式新创建的也生效。
session 1：未来访问test模式下所有新建的表赋权，创建 t5 表。
postgres=# alter default privileges in schema test grant select on tables to readonly ; ALTER DEFAULT PRIVILEGES postgres=# create table test.t5 as select * from test.emp; CREATE TABLE
session 2：查询readonly用户
postgres=> select * from test.t5; empno | ename | job | mgr | hiredate | sal | comm | deptno -------+--------+-----------+------+------------+---------+---------+-------- 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | | 20 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | | 30 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | | 10 7839 | KING | PRESIDENT | | 1981-11-17 | 5000.00 | | 10 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | | 30 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | | 20 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | | 10 7788 | test | ANALYST | 7566 | 1982-12-09 | 3000.00 | | 20 7876 | ADAMS | CLERK | 7788 | 1983-01-12 | 1100.00 | | 20 1111 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | | 20 (14 rows)
--创建影子用户 create user readonly with password 'postgres'; --将schema中usage权限赋予给readonly用户,访问所有已存在的表 grant usage on schema test to readonly; grant select on all tables in schema test to readonly; --未来访问test模式下所有新建的表 alter default privileges in schema test grant select on tables to readonly ;
