前言：
postgresql做为一个比较复杂的关系型的重型数据库，不管是安装部署，还是后期的运行维护，都还是有比较多的细节问题需要引起关注。
例如，用户权限的合理分配，那么，什么是权限的合理分配呢？ 自然是权限的最小化原则，也就是说每个用户能够完成其权限范围内的工作，而不会由于黑客攻击，漏洞等原因造成安全方面的危险。
在写这篇文章之前，仅仅是对于一些普通用户简单的随便赋权就完事了，而这样的管理工作显然是不够的，因此，本文将对postgresql数据库内的用户赋权和去权做一个相对完整的总结，并通过示例说明 usage权限和select权限的不同。
一，
用户的权限有哪些？
OK，增删改查也就是select ，update，insert，delete 和usage应该是可以归于一类的，而select和usage是十分相似的，至少在schema下，两者是基本雷同的，但需要注意的是，授权后的新建对象，比如新建表，usage是无权查询的，而select显然是不存在此类问题的。
二，
正确的只读用户赋权
1，
第一种赋权
usage---使用权+select查询权
先创建相关schema，名为mytest，相关role，名为test
test=# \c test
You are now connected to database "test" as user "postgres".
test=# create schema mytest;
CREATE SCHEMA
test=# \du
List of roles
Role name | Attributes | Member of
--------------------+------------------------------------------------------------+-----------
drmc | | {}
pg1 | Superuser, Create role, Create DB, Replication, Bypass RLS | {}
pms30 | Superuser, Create role, Create DB, Replication, Bypass RLS | {}
postgres | Superuser | {}
postgres_exporter | | {}
postgres_exporter1 | | {}
power_common | | {}
power_tf | | {}
zsk | | {}
test=# create user test with password '123456';
CREATE ROLE
赋权：
test=# grant USAGE on SCHEMA mytest to test;
GRANT
test1=> grant SELECT on ALL tables in schema mytest to test;
测试就不演示了，只是需要注意一点，要赋权两个，usage和select，两者缺一不可，也就是说必须是两个命令！！！！！
OK，以上是用户test赋权select到test数据库下的mytest这个schema，下面为了继续测试，删除test这个用户。
2，
强制删除已赋权过的用户
OK，删除的时候报错了，这就让人比较无语了，报错说的是名为test的数据库有5个对象依赖于用户test，不过还是有解决办法的
postgres=# drop user test;
2023-08-09 01:15:34.031 CST [14975] ERROR: role "test" cannot be dropped because some objects depend on it
2023-08-09 01:15:34.031 CST [14975] DETAIL: 5 objects in database test
2023-08-09 01:15:34.031 CST [14975] STATEMENT: drop user test;
ERROR: role "test" cannot be dropped because some objects depend on it
DETAIL: 5 objects in database test
强制删除：
需要reassign和drop owner by以及drop user 三条命令，缺一不可。
postgres=# \c test
You are now connected to database "test" as user "postgres".
test=# \dn
List of schemas
Name | Owner
--------+-------
mytest | test
public | pg1
(2 rows)
test=# REASSIGN OWNED BY test TO postgres;
REASSIGN OWNED
test=# \dn
List of schemas
Name | Owner
--------+----------
mytest | postgres
public | pg1
(2 rows)
test=# drop owned BY test cascade;
NOTICE: drop cascades to 4 other objects
DETAIL: drop cascades to table mytest.dept
drop cascades to table mytest.emp
drop cascades to table mytest.bonus
drop cascades to table mytest.salgrade
DROP OWNED
OK，查询test这个用户是否删除：
可以看到，确实没有了，有强迫症的人士就非常舒服了。
但特别需要注意，该强制删除用户因为是级联删除，因此，很大概率会把依赖的schema和table都删除，所以此方式强制删除用户需要提前备份，防止发生不测。
test1=# \du+
List of roles
Role name | Attributes | Member of | Description
--------------------+------------------------------------------------------------+-----------+-------------
drmc | | {} |
pg1 | Superuser, Create role, Create DB, Replication, Bypass RLS | {} |
pms30 | Superuser, Create role, Create DB, Replication, Bypass RLS | {} |
postgres | Superuser | {} |
postgres_exporter | | {} |
postgres_exporter1 | | {} |
power_common | | {} |
power_tf | | {} |
zsk | | {} |
3，
第二种赋权
grant select+ owner
test=# create user test with password '123456';
CREATE ROLE
test=# \c
You are now connected to database "test" as user "postgres".
test=# grant SELECT on ALL tables in schema mytest to test;
GRANT
test=# set search_path to mytest ;
SET
test=# alter schema mytest owner to test;
ALTER SCHEMA
测试：
test=> \c
You are now connected to database "test" as user "test".
test=> set search_path to mytest ;
SET
test=> \dp
Access privileges
Schema | Name | Type | Access privileges | Column privileges | Policies
--------+----------+-------+---------------------------+-------------------+----------
mytest | bonus | table | postgres=arwdDxt/postgres+| |
| | | test=r/postgres | |
mytest | dept | table | postgres=arwdDxt/postgres+| |
| | | test=r/postgres | |
mytest | emp | table | postgres=arwdDxt/postgres+| |
| | | test=r/postgres | |
mytest | salgrade | table | postgres=arwdDxt/postgres+| |
| | | test=r/postgres | |
(4 rows)
test=> \dn
List of schemas
Name | Owner
--------+-------
mytest | test
public | pg1
(2 rows)
test=> set search_path to mytest ;
SET
test=> select * from emp;
empno | ename | job | mgr | hiredate | sal | comm | deptno
-------+--------+-----------+------+------------+---------+---------+--------
7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | | 20
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
7788 | SCOTT | ANALYST | 7566 | 0087-04-19 | 3000.00 | | 20
7839 | KING | PRESIDENT | | 1981-11-17 | 5000.00 | | 10
7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30
7876 | ADAMS | CLERK | 7788 | 0087-05-23 | 1100.00 | | 20
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
(14 rows)