Provided by: postgresql-client-10_10.23-0ubuntu0.18.04.2_amd64 
NAME
CREATE_POLICY - define a new row level security policy for a table
SYNOPSIS
CREATE 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 ) ]
[ WITH CHECK ( check_expression ) ]
DESCRIPTION
The CREATE POLICY command defines a new row-level security policy for a table. Note that
row-level security must be enabled on the table (using ALTER TABLE ... ENABLE ROW LEVEL
SECURITY) in order for created policies to be applied.
A policy grants the permission to select, insert, update, or delete rows that match the
relevant policy expression. Existing table rows are checked against the expression
specified in USING, while new rows that would be created via INSERT or UPDATE are checked
against the expression specified in WITH CHECK. When a USING expression returns true for a
given row then that row is visible to the user, while if false or null is returned then
the row is not visible. When a WITH CHECK expression returns true for a row then that row
is inserted or updated, while if false or null is returned then an error occurs.
For INSERT and UPDATE statements, WITH CHECK expressions are enforced after BEFORE
triggers are fired, and before any actual data modifications are made. Thus a BEFORE ROW
trigger may modify the data to be inserted, affecting the result of the security policy
check. WITH CHECK expressions are enforced before any other constraints.
Policy names are per-table. Therefore, one policy name can be used for many different
tables and have a definition for each table which is appropriate to that table.
Policies can be applied for specific commands or for specific roles. The default for newly
created policies is that they apply for all commands and roles, unless otherwise
specified. Multiple policies may apply to a single command; see below for more details.
Table 241 summarizes how the different types of policy apply to specific commands.
For policies that can have both USING and WITH CHECK expressions (ALL and UPDATE), if no
WITH CHECK expression is defined, then the USING expression will be used both to determine
which rows are visible (normal USING case) and which new rows will be allowed to be added
(WITH CHECK case).
If row-level security is enabled for a table, but no applicable policies exist, a “default
deny” policy is assumed, so that no rows will be visible or updatable.
PARAMETERS
name
The name of the policy to be created. This must be distinct from the name of any other
policy for the table.
table_name
The name (optionally schema-qualified) of the table the policy applies to.
PERMISSIVE
Specify that the policy is to be created as a permissive policy. All permissive
policies which are applicable to a given query will be combined together using the
Boolean “OR” operator. By creating permissive policies, administrators can add to the
set of records which can be accessed. Policies are permissive by default.
RESTRICTIVE
Specify that the policy is to be created as a restrictive policy. All restrictive
policies which are applicable to a given query will be combined together using the
Boolean “AND” operator. By creating restrictive policies, administrators can reduce
the set of records which can be accessed as all restrictive policies must be passed
for each record.
Note that there needs to be at least one permissive policy to grant access to records
before restrictive policies can be usefully used to reduce that access. If only
restrictive policies exist, then no records will be accessible. When a mix of
permissive and restrictive policies are present, a record is only accessible if at
least one of the permissive policies passes, in addition to all the restrictive
policies.
command
The command to which the policy applies. Valid options are ALL, SELECT, INSERT,
UPDATE, and DELETE. ALL is the default. See below for specifics regarding how these
are applied.
role_name
The role(s) to which the policy is to be applied. The default is PUBLIC, which will
apply the policy to all roles.
using_expression
Any SQL conditional expression (returning boolean). The conditional expression cannot
contain any aggregate or window functions. This expression will be added to queries
that refer to the table if row level security is enabled. Rows for which the
expression returns true will be visible. Any rows for which the expression returns
false or null will not be visible to the user (in a SELECT), and will not be available
for modification (in an UPDATE or DELETE). Such rows are silently suppressed; no error
is reported.
check_expression
Any SQL conditional expression (returning boolean). The conditional expression cannot
contain any aggregate or window functions. This expression will be used in INSERT and
UPDATE queries against the table if row level security is enabled. Only rows for which
the expression evaluates to true will be allowed. An error will be thrown if the
expression evaluates to false or null for any of the records inserted or any of the
records that result from the update. Note that the check_expression is evaluated
against the proposed new contents of the row, not the original contents.
Per-Command Policies
ALL
Using ALL for a policy means that it will apply to all commands, regardless of the
type of command. If an ALL policy exists and more specific policies exist, then both
the ALL policy and the more specific policy (or policies) will be applied.
Additionally, ALL policies will be applied to both the selection side of a query and
the modification side, using the USING expression for both cases if only a USING
expression has been defined.
As an example, if an UPDATE is issued, then the ALL policy will be applicable both to
what the UPDATE will be able to select as rows to be updated (applying the USING
expression), and to the resulting updated rows, to check if they are permitted to be
added to the table (applying the WITH CHECK expression, if defined, and the USING
expression otherwise). If an INSERT or UPDATE command attempts to add rows to the
table that do not pass the ALL policy's WITH CHECK expression, the entire command will
be aborted.
SELECT
Using SELECT for a policy means that it will apply to SELECT queries and whenever
SELECT permissions are required on the relation the policy is defined for. The result
is that only those records from the relation that pass the SELECT policy will be
returned during a SELECT query, and that queries that require SELECT permissions, such
as UPDATE, will also only see those records that are allowed by the SELECT policy. A
SELECT policy cannot have a WITH CHECK expression, as it only applies in cases where
records are being retrieved from the relation.
INSERT
Using INSERT for a policy means that it will apply to INSERT commands. Rows being
inserted that do not pass this policy will result in a policy violation error, and the
entire INSERT command will be aborted. An INSERT policy cannot have a USING
expression, as it only applies in cases where records are being added to the relation.
Note that INSERT with ON CONFLICT DO UPDATE checks INSERT policies' WITH CHECK
expressions only for rows appended to the relation by the INSERT path.
UPDATE
Using UPDATE for a policy means that it will apply to UPDATE, SELECT FOR UPDATE and
SELECT FOR SHARE commands, as well as auxiliary ON CONFLICT DO UPDATE clauses of
INSERT commands. Since UPDATE involves pulling an existing record and replacing it
with a new modified record, UPDATE policies accept both a USING expression and a WITH
CHECK expression. The USING expression determines which records the UPDATE command
will see to operate against, while the WITH CHECK expression defines which modified
rows are allowed to be stored back into the relation.
Any rows whose updated values do not pass the WITH CHECK expression will cause an
error, and the entire command will be aborted. If only a USING clause is specified,
then that clause will be used for both USING and WITH CHECK cases.
Typically an UPDATE command also needs to read data from columns in the relation being
updated (e.g., in a WHERE clause or a RETURNING clause, or in an expression on the
right hand side of the SET clause). In this case, SELECT rights are also required on
the relation being updated, and the appropriate SELECT or ALL policies will be applied
in addition to the UPDATE policies. Thus the user must have access to the row(s) being
updated through a SELECT or ALL policy in addition to being granted permission to
update the row(s) via an UPDATE or ALL policy.
When an INSERT command has an auxiliary ON CONFLICT DO UPDATE clause, if the UPDATE
path is taken, the row to be updated is first checked against the USING expressions of
any UPDATE policies, and then the new updated row is checked against the WITH CHECK
expressions. Note, however, that unlike a standalone UPDATE command, if the existing
row does not pass the USING expressions, an error will be thrown (the UPDATE path will
never be silently avoided).
DELETE
Using DELETE for a policy means that it will apply to DELETE commands. Only rows that
pass this policy will be seen by a DELETE command. There can be rows that are visible
through a SELECT that are not available for deletion, if they do not pass the USING
expression for the DELETE policy.
In most cases a DELETE command also needs to read data from columns in the relation
that it is deleting from (e.g., in a WHERE clause or a RETURNING clause). In this
case, SELECT rights are also required on the relation, and the appropriate SELECT or
ALL policies will be applied in addition to the DELETE policies. Thus the user must
have access to the row(s) being deleted through a SELECT or ALL policy in addition to
being granted permission to delete the row(s) via a DELETE or ALL policy.
A DELETE policy cannot have a WITH CHECK expression, as it only applies in cases where
records are being deleted from the relation, so that there is no new row to check.
Table 241. Policies Applied by Command Type
┌───────────────┬────────────────┬────────────┬───────────────────────────┬──────────────┐
│ │ SELECT/ALL │ INSERT/ALL │ UPDATE/ALL policy │ DELETE/ALL │
│ │ policy │ policy │ │ policy │
│Command ├────────────────┼────────────┼──────────────┬────────────┼──────────────┤
│ │ USING │ WITH CHECK │ USING │ WITH CHECK │ USING │
│ │ expression │ expression │ expression │ expression │ expression │
├───────────────┼────────────────┼────────────┼──────────────┼────────────┼──────────────┤
│SELECT │ Existing row │ — │ — │ — │ — │
├───────────────┼────────────────┼────────────┼──────────────┼────────────┼──────────────┤
│SELECT FOR │ Existing row │ — │ Existing row │ — │ — │
│UPDATE/SHARE │ │ │ │ │ │
├───────────────┼────────────────┼────────────┼──────────────┼────────────┼──────────────┤
│INSERT │ — │ New row │ — │ — │ — │
├───────────────┼────────────────┼────────────┼──────────────┼────────────┼──────────────┤
│INSERT ... │ New row [a] │ New row │ — │ — │ — │
│RETURNING │ │ │ │ │ │
├───────────────┼────────────────┼────────────┼──────────────┼────────────┼──────────────┤
│UPDATE │ Existing & new │ — │ Existing row │ New row │ — │
│ │ rows [a] │ │ │ │ │
├───────────────┼────────────────┼────────────┼──────────────┼────────────┼──────────────┤
│DELETE │ Existing row │ — │ — │ — │ Existing row │
│ │ [a] │ │ │ │ │
├───────────────┼────────────────┼────────────┼──────────────┼────────────┼──────────────┤
│ON CONFLICT DO │ Existing & new │ — │ Existing row │ New row │ — │
│UPDATE │ rows │ │ │ │ │
├───────────────┴────────────────┴────────────┴──────────────┴────────────┴──────────────┤
│---- │
│[a] If read access is required to the existing or new row (for example, a WHERE or │
│RETURNING clause that refers to columns from the relation). │
└────────────────────────────────────────────────────────────────────────────────────────┘
Application of Multiple Policies
When multiple policies of different command types apply to the same command (for example,
SELECT and UPDATE policies applied to an UPDATE command), then the user must have both
types of permissions (for example, permission to select rows from the relation as well as
permission to update them). Thus the expressions for one type of policy are combined with
the expressions for the other type of policy using the AND operator.
When multiple policies of the same command type apply to the same command, then there must
be at least one PERMISSIVE policy granting access to the relation, and all of the
RESTRICTIVE policies must pass. Thus all the PERMISSIVE policy expressions are combined
using OR, all the RESTRICTIVE policy expressions are combined using AND, and the results
are combined using AND. If there are no PERMISSIVE policies, then access is denied.
Note that, for the purposes of combining multiple policies, ALL policies are treated as
having the same type as whichever other type of policy is being applied.
For example, in an UPDATE command requiring both SELECT and UPDATE permissions, if there
are multiple applicable policies of each type, they will be combined as follows:
expression from RESTRICTIVE SELECT/ALL policy 1
AND
expression from RESTRICTIVE SELECT/ALL policy 2
AND
...
AND
(
expression from PERMISSIVE SELECT/ALL policy 1
OR
expression from PERMISSIVE SELECT/ALL policy 2
OR
...
)
AND
expression from RESTRICTIVE UPDATE/ALL policy 1
AND
expression from RESTRICTIVE UPDATE/ALL policy 2
AND
...
AND
(
expression from PERMISSIVE UPDATE/ALL policy 1
OR
expression from PERMISSIVE UPDATE/ALL policy 2
OR
...
)
NOTES
You must be the owner of a table to create or change policies for it.
While policies will be applied for explicit queries against tables in the database, they
are not applied when the system is performing internal referential integrity checks or
validating constraints. This means there are indirect ways to determine that a given value
exists. An example of this is attempting to insert a duplicate value into a column that is
a primary key or has a unique constraint. If the insert fails then the user can infer that
the value already exists. (This example assumes that the user is permitted by policy to
insert records which they are not allowed to see.) Another example is where a user is
allowed to insert into a table which references another, otherwise hidden table. Existence
can be determined by the user inserting values into the referencing table, where success
would indicate that the value exists in the referenced table. These issues can be
addressed by carefully crafting policies to prevent users from being able to insert,
delete, or update records at all which might possibly indicate a value they are not
otherwise able to see, or by using generated values (e.g., surrogate keys) instead of keys
with external meanings.
Generally, the system will enforce filter conditions imposed using security policies prior
to qualifications that appear in user queries, in order to prevent inadvertent exposure of
the protected data to user-defined functions which might not be trustworthy. However,
functions and operators marked by the system (or the system administrator) as LEAKPROOF
may be evaluated before policy expressions, as they are assumed to be trustworthy.
Since policy expressions are added to the user's query directly, they will be run with the
rights of the user running the overall query. Therefore, users who are using a given
policy must be able to access any tables or functions referenced in the expression or they
will simply receive a permission denied error when attempting to query the table that has
row-level security enabled. This does not change how views work, however. As with normal
queries and views, permission checks and policies for the tables which are referenced by a
view will use the view owner's rights and any policies which apply to the view owner.
Additional discussion and practical examples can be found in Section 5.7.
COMPATIBILITY
CREATE POLICY is a PostgreSQL extension.
SEE ALSO
ALTER POLICY (ALTER_POLICY(7)), DROP POLICY (DROP_POLICY(7)), ALTER TABLE (ALTER_TABLE(7))