PostgreSQL中的默认权限(default privileges)

有时候我们会遇到这种情况(这种情况并不少见)：用户schema中有很多对象，并且你想授权题用户访问这些表。你可以通过grant直接授权，但是当对象属主创建新的对象呢？你可能还需要再次授权，但是postgresql提供一个解决方案。

postgres=# create user a password 'a';
CREATE ROLE
postgres=# grant connect on database postgres to a;
GRANT
postgres=# create schema a authorization a;
CREATE SCHEMA
postgres=# alter user a set search_path=a;
ALTER ROLE
postgres=# create user b password 'b';
CREATE ROLE
postgres=# grant connect on database postgres to b;
GRANT
postgres=# create schema b authorization b;
CREATE SCHEMA
postgres=# alter user b set search_path=b;
ALTER ROLE
postgres=# du
                                   List of roles
 Role name |                         Attributes                         | Member of
-----------+------------------------------------------------------------+-----------
 a         |                                                            | {}
 b         |                                                            | {}
 postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS | {}

postgres=# dn
  List of schemas
  Name  |  Owner
--------+----------
 a      | a
 b      | b
 public | postgres
(3 rows)

postgres=#

　

这里用户a是对象的属主。创建两张表：

postgres=> c postgres a
You are now connected to database "postgres" as user "a".
postgres=> create table t1(a int);
CREATE TABLE
postgres=> create table t2(a int);
CREATE TABLE
postgres=> insert into t1(a) values(1);
INSERT 0 1
postgres=> insert into t2(a) values(2);
INSERT 0 1
postgres=> d
       List of relations
 Schema | Name | Type  | Owner 
--------+------+-------+-------
 a      | t1   | table | a
 a      | t2   | table | a
(2 rows)

postgres=> 

　　

给用户b授权：

postgres=> grant select on table t1 to b;
GRANT
postgres=> grant select on table t2 to b;
GRANT
postgres=> 

　　

现在用户b是否可以查看a所创键的表的内容呢？

postgres=> c postgres b
You are now connected to database "postgres" as user "b".
postgres=> select count(*) from a.t1;
ERROR:  permission denied for schema a
LINE 1: select count(*) from a.t1;
                             ^
postgres=> 

这里还需要给b授权访问schema a的权限：

postgres=> c postgres a
You are now connected to database "postgres" as user "a".
postgres=> grant usage on schema a to b;
GRANT
postgres=> 

这里只是授权b访问schema a的权限，并不是授权访问里面的表。

postgres=> c postgres b
You are now connected to database "postgres" as user "b".
postgres=> select count(*) from a.t1;
 count 
-------
     1
(1 row)

postgres=> select count(*) from a.t2;
 count 
-------
     1
(1 row)

postgres=> 

　　

现在a再创建一个新表：

postgres=> c postgres a
You are now connected to database "postgres" as user "a".
postgres=> create table t3 as select * from t1;
SELECT 1
postgres=> d
               List of relations
 Schema |      Name      |   Type   |  Owner   
--------+----------------+----------+----------
 public | t1             | table    | a
 public | t2             | table    | a
 public | t3             | table    | a
(3 rows)

postgres=> 

　　

再次尝试使用b访问t3表：

postgres=> c postgres b
You are now connected to database "postgres" as user "b".
postgres=> select count(*) from a.t3;
ERROR:  permission denied for table a.t3
postgres=> 

　　

现在修改一下default privileges：

postgres=> c postgres a
You are now connected to database "postgres" as user "a".
postgres=# alter default privileges in schema a grant select on tables to b;
ALTER DEFAULT PRIVILEGES
postgres=# 

　　

那现在b可以访问表t3了吗？

postgres=# c postgres b
You are now connected to database "postgres" as user "b".
postgres=> select count(*) from a.t3;
ERROR:  permission denied for table a.t3
postgres=> 

还是不可以，修改了default privileges之后，只是对授权之后创建的对象有效。

 

现在a用户再创建表t4：

postgres=# c postgres a
You are now connected to database "postgres" as user "a".
postgres=> create table t4 as select from t1;
SELECT 1
postgres=> 

　　

再次看看b是否查看表t4：

postgres=> c postgres b
You are now connected to database "postgres" as user "b".
postgres=> select count(*) from a.t4;
 count 
-------
     1
(1 row)

postgres=>