在實際的生產環境 ，我們經常會碰到這樣的情況：因為業務場景需要，本部門某些重要的業務數據表需要給予其他部門查看權限，因業務的擴展及調整，后期可能需要放開更多的表查詢權限。為解決此種業務需求，我們可以采用創建視圖的方式來解決，已可以通過創建影子用戶的方式來滿足需求，本文主要介紹影子用戶的創建及授權方法。
場景1：只授予usage on schema 權限
session 1:
--創建readonly用戶，并將test模式賦予readonly用戶。
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:
--登陸readonly用戶可以查詢test模式下現存的所有表。
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)
換到session 1創建新表t1
postgres=# create table test.t1 as select * from test.emp;
CREATE TABLE
切換到session 2 readonly用戶下，t1表無法查詢
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
結論：如果只授予 usage on schema 權限，readonly 只能查看 test 模式下已經存在的表和對象。在授予 usage on schema 權限之后創建的新表無法查看。
場景2：授予usage on schema 權限之后，再賦予 select on all tables in schema 權限
針對上個場景session 2 **ERROR: permission denied for table t1 錯誤的處理
postgres=> select * from test.t1 ;
**ERROR: permission denied for table t1
session 1： 使用postgres用戶授予readonly用戶 select on all tables 權限
postgres=# grant select on all tables in schema test TO readonly ;
session 2: readonly用戶查詢 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用戶的test模式下創建新表 t2
postgres=# create table test.t2 as select * from test.emp;
SELECT 14
session 2：readonly用戶查詢 t2 表權限不足
postgres=> select * from test.t2 ;
ERROR: permission denied for table t2
session 1：再次賦予 grant select on all tables
postgres=# grant select on all tables in schema test TO readonly ;
session 2：readonly用戶又可以查看 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)
影子用戶創建
如果想讓readonly只讀用戶不在每次 postgres用戶在test模式中創建新表后都要手工賦予 grant select on all tables in schema test TO readonly 權限。則需要授予對test默認的訪問權限，對于test模式新創建的也生效。
session 1：未來訪問test模式下所有新建的表賦權，創建 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：查詢readonly用戶
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)
總結：影子用戶創建的步驟
--創建影子用戶
create user readonly with password 'postgres';
--將schema中usage權限賦予給readonly用戶,訪問所有已存在的表
grant usage on schema test to readonly;
grant select on all tables in schema test to readonly;
--未來訪問test模式下所有新建的表
alter default privileges in schema test grant select on tables to readonly ;
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