# ALTER ROW LEVEL SECURITY POLICY
#### 功能描述
对已存在的行访问控制策略（包括行访问控制策略的名称，行访问控制指定的用户，行访问控制的策略表达式）进行修改。
#### 注意事项
表的所有者或管理员用户才能进行此操作。
#### 语法格式
```
ALTER [ ROW LEVEL SECURITY ] POLICY [ IF EXISTS ] policy_name ON table_name RENAME TO new_policy_name;
ALTER [ ROW LEVEL SECURITY ] POLICY policy_name ON table_name
    [ TO { role_name | PUBLIC } [, ...] ]
    [ USING ( using_expression ) ];
```
#### 参数说明
- policy_name 行访问控制策略名称。
  
- table_name 行访问控制策略的表名。
  
- new_policy_name 新的行访问控制策略名称。
  
- role_name 行访问控制策略应用的数据库用户，可以指定多个用户，PUBLIC表示应用到所有用户。
  
- using_expression 行访问控制的表达式，返回值为boolean类型。
  
 
#### 示例
```
--创建数据表all_data。
openGauss=# CREATE TABLE all_data(id int, role varchar(100), data varchar(100));
--创建行访问控制策略，当前用户只能查看用户自身的数据。
openGauss=# CREATE ROW LEVEL SECURITY POLICY all_data_rls ON all_data USING(role = CURRENT_USER);
openGauss=# \d+ all_data
                               Table "public.all_data"
 Column |          Type          | Modifiers | Storage  | Stats target | Description
--------+------------------------+-----------+----------+--------------+-------------
 id     | integer                |           | plain    |              |
 role   | character varying(100) |           | extended |              |
 data   | character varying(100) |           | extended |              |
Row Level Security Policies:
    POLICY "all_data_rls"
      USING (((role)::name = "current_user"()))
Has OIDs: no
Location Nodes: ALL DATANODES
Options: orientation=row
--创建用户alice、bob。
openGauss=# CREATE ROLE alice WITH PASSWORD "********";
openGauss=# CREATE ROLE bob WITH PASSWORD "********";
--修改行访问控制all_data_rls的名称。
openGauss=# ALTER ROW LEVEL SECURITY POLICY all_data_rls ON all_data RENAME TO all_data_new_rls;
--修改行访问控制策略影响的用户。
openGauss=# ALTER ROW LEVEL SECURITY POLICY all_data_new_rls ON all_data TO alice, bob;
openGauss=# \d+ all_data
                               Table "public.all_data"
 Column |          Type          | Modifiers | Storage  | Stats target | Description
--------+------------------------+-----------+----------+--------------+-------------
 id     | integer                |           | plain    |              |
 role   | character varying(100) |           | extended |              |
 data   | character varying(100) |           | extended |              |
Row Level Security Policies:
    POLICY "all_data_new_rls"
      TO alice,bob
      USING (((role)::name = "current_user"()))
Has OIDs: no
Location Nodes: ALL DATANODES
Options: orientation=row, enable_rowsecurity=true
--修改行访问控制策略表达式。
openGauss=# ALTER ROW LEVEL SECURITY POLICY all_data_new_rls ON all_data USING (id > 100 AND role = current_user);
openGauss=# \d+ all_data
                               Table "public.all_data"
 Column |          Type          | Modifiers | Storage  | Stats target | Description
--------+------------------------+-----------+----------+--------------+-------------
 id     | integer                |           | plain    |              |
 role   | character varying(100) |           | extended |              |
 data   | character varying(100) |           | extended |              |
Row Level Security Policies:
    POLICY "all_data_new_rls"
      TO alice,bob
      USING (((id > 100) AND ((role)::name = "current_user"())))
Has OIDs: no
Location Nodes: ALL DATANODES
Options: orientation=row, enable_rowsecurity=true
--删除用户alice, bob。
openGauss=# DROP ROLE alice, bob;
--删除访问控制策略。
openGauss=# DROP ROW LEVEL SECURITY POLICY all_data_new_rls ON all_data;
--删除数据表all_data。
openGauss=# DROP TABLE all_data;
```
#### 相关链接
[CREATE ROW LEVEL SECURITY POLICY](https://support.huaweicloud.com/centralized-devg-v2-gaussdb/gaussdb_42_0418.html#ZH-CN_TOPIC_0000002221496313)，[DROP ROW LEVEL SECURITY POLICY](https://support.huaweicloud.com/centralized-devg-v2-gaussdb/gaussdb_42_0458.html#ZH-CN_TOPIC_0000002221496361)