CREATE ROW LEVEL SECURITY POLICY

Function

CREATE ROW LEVEL SECURITY POLICY creates a row-level access control policy for a table.

The policy takes effect only after row-level access control is enabled (by running ALTER TABLE… ENABLE ROW LEVEL SECURITY). Otherwise, this statement does not take effect.

Currently, row-level access control affects the read (SELECT, UPDATE, DELETE) of data tables and does not affect the write (INSERT and MERGE INTO) of data tables. The table owner or system administrators can create an expression in the USING clause. When the client reads the data table, the database server combines the expressions that meet the condition and applies it to the execution plan in the statement rewriting phase of a query. For each tuple in a data table, if the expression returns TRUE, the tuple is visible to the current user; if the expression returns FALSE or NULL, the tuple is invisible to the current user.

A row-level access control policy name is specific to a table. A data table cannot have row-level access control policies with the same name. Different data tables can have the same row-level access control policy.

Row-level access control policies can be applied to specified operations (SELECT, UPDATE, DELETE, and ALL). ALL indicates that SELECT, UPDATE, and DELETE will be affected. For a new row-level access control policy, the default value ALL will be used if you do not specify the operations that will be affected.

Row-level access control policies can be applied to a specified user (role) or to all users (PUBLIC). For a new row-level access control policy, the default value PUBLIC will be used if you do not specify the user that will be affected.

Precautions

• Row-level access control policies can be defined for row-store tables, row-store partitioned tables, column-store tables, column-store partitioned tables, unlogged tables, and hash tables.
• Row-level access control policies cannot be defined for foreign tables and local temporary tables.
• Row-level access control policies cannot be defined for views.
• A maximum of 100 row-level access control policies can be defined for a table.
• System administrators are not affected by row-level access control policies and can view all data in a table.
• Tables queried by using SQL statements, views, functions, and stored procedures are affected by row-level access control policies.

Syntax

CREATE [ ROW LEVEL SECURITY ] POLICY policy_name ON table_name
     [ AS { PERMISSIVE | RESTRICTIVE } ]
     [ FOR { ALL | SELECT | INSERT | UPDATE | DELETE } ]
     [ TO { role_name | PUBLIC | CURRENT_USER | SESSION_USER } [, ...] ]
     USING ( using_expression )

Parameter Description

• policy_name

  Specifies the name of a row-level access control policy to be created. The names of row-level access control policies for a table must be unique.

• table_name

  Specifies the name of a table to which a row-level access control policy is applied.

• PERMISSIVE | RESTRICTIVE

  PERMISSIVE enables the permissive policy for row-level access control. The conditions of the permissive policy are joined through the OR expression.

  RESTRICTIVE enables the restrictive policy for row-level access control. The conditions of the restrictive policy are joined through the AND expression. The join methods are as follows:

  (using_expression_permissive_1 OR using_expression_permissive_2 ...) AND (using_expression_restrictive_1 AND using_expression_restrictive_2 ...)

  The default value is PERMISSIVE.

• command

  Specifies the SQL operations affected by a row-level access control policy, including ALL, SELECT, UPDATE, and DELETE. If this parameter is not specified, the default value ALL will be used, covering SELECT, UPDATE, and DELETE.

  If command is set to SELECT, only tuple data that meets the condition (the return value of using_expression is TRUE) can be queried. The operations that are affected include SELECT, UPDATE…. RETURNING, and DELETE… RETURNING.

  If command is set to UPDATE, only tuple data that meets the condition (the return value of using_expression is TRUE) can be updated. The operations that are affected include UPDATE, UPDATE … RETURNING, and SELECT … FOR UPDATE/SHARE.

  If command is set to DELETE, only tuple data that meets the condition (the return value of using_expression is TRUE) can be deleted. The operations that are affected include DELETE and DELETE … RETURNING.

  The following table describes the relationship between row-level access control policies and SQL statements.

  Table 1 Relationship between row-level access control policies and SQL statements

  Command	SELECT/ALL policy	UPDATE/ALL policy	DELETE/ALL policy
  SELECT	Existing row	No	No
  SELECT FOR UPDATE/SHARE	Existing row	Existing row	No
  UPDATE	No	Existing row	No
  UPDATE RETURNING	Existing row	Existing row	No
  DELETE	No	No	Existing row
  DELETE RETURNING	Existing row	No	Existing row

• role_name

  Specifies database users affected by a row-level access control policy.

  If this parameter is not specified, the default value PUBLIC will be used, indicating that all database users will be affected. You can specify multiple affected database users.

  NOTICE: System administrators are not affected by row access control.

• using_expression

  Specifies an expression defined for a row-level access control policy (return type: boolean).

  The expression cannot contain aggregate functions or window functions. In the statement rewriting phase of a query, if row-level access control for a data table is enabled, the expressions that meet the specified conditions will be added to the plan tree. The expression is calculated for each tuple in the data table. For SELECT, UPDATE, and DELETE, row data is visible to the current user only when the return value of the expression is TRUE. If the expression returns FALSE, the tuple is invisible to the current user. In this case, the user cannot view the tuple through the SELECT statement, update the tuple through the UPDATE statement, or delete the tuple through the DELETE statement.

Example

-- Create user alice.
mogdb=# CREATE USER alice PASSWORD 'Gauss@123';

-- Create user bob.
mogdb=# CREATE USER bob PASSWORD 'Gauss@123';

-- Create the data table all_data.
mogdb=# CREATE TABLE all_data(id int, role varchar(100), data varchar(100));

--Insert data into the data table.
mogdb=# INSERT INTO all_data VALUES(1, 'alice', 'alice data');
mogdb=# INSERT INTO all_data VALUES(2, 'bob', 'bob data');
mogdb=# INSERT INTO all_data VALUES(3, 'peter', 'peter data');

-- Grant the read permission on the all_data table to users alice and bob.
mogdb=# GRANT SELECT ON all_data TO alice, bob;

--Enable row-level access control.
mogdb=# ALTER TABLE all_data ENABLE ROW LEVEL SECURITY;

--Create a row-level access control policy to specify that the current user can view only their own data.
mogdb=# CREATE ROW LEVEL SECURITY POLICY all_data_rls ON all_data USING(role = CURRENT_USER);

-- View information about the all_data table.
mogdb=# \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
Options: orientation=row, compression=no, enable_rowsecurity=true

-- Run SELECT.
mogdb=# SELECT * FROM all_data;
 id | role  |    data
----+-------+------------
  1 | alice | alice data
  2 | bob   | bob data
  3 | peter | peter data
(3 rows)

mogdb=# EXPLAIN(COSTS OFF) SELECT * FROM all_data;
      QUERY PLAN
----------------------
 Seq Scan on all_data
(1 row)

-- Switch to user alice and run SELECT.
mogdb=# SELECT * FROM all_data;
 id | role  |    data
----+-------+------------
  1 | alice | alice data
(1 row)

mogdb=# EXPLAIN(COSTS OFF) SELECT * FROM all_data;
 QUERY PLAN
----------------------------------------------------------------
 Seq Scan on all_data
   Filter: ((role)::name = 'alice'::name)
 Notice: This query is influenced by row level security feature
(3 rows)