CREATE POLICY(7) PostgreSQL 9.5.0 Documentation CREATE POLICY(7)NAMECREATE_POLICY - define a new row level security policy for a table
SYNOPSIS
CREATE POLICY name ON table_name
[ 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. If multiple policies
apply to a given statement, they will be combined using OR (although ON
CONFLICT DO UPDATE and INSERT policies are not combined in this way,
but rather enforced as noted at each stage of ON CONFLICT execution).
For commands that can have both USING and WITH CHECK policies (ALL and
UPDATE), if no WITH CHECK policy is defined, then the USING policy will
be used both for which rows are visible (normal USING case) and for
which 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.
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 combined using OR, as usual
for overlapping policies. 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
commands (or auxiliary ON CONFLICT DO UPDATE clauses of INSERT
commands). Since UPDATE involves pulling an existing record and
then making changes to some portion (but possibly not all) of the
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.
When an UPDATE command is used with a WHERE clause or a RETURNING
clause, SELECT rights are also required on the relation being
updated and the appropriate SELECT and ALL policies will be
combined (using OR for any overlapping SELECT related policies
found) with the USING clause of the UPDATE policy using AND.
Therefore, in order for a user to be able to UPDATE specific rows,
the user must have access to the row(s) through a SELECT or ALL
policy and the row(s) must pass the UPDATE policy's USING
expression.
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.
Note, however, that INSERT with ON CONFLICT DO UPDATE requires that
an UPDATE policy USING expression always be enforced as a WITH
CHECK expression. This UPDATE policy must always pass when the
UPDATE path is taken. Any existing row that necessitates that the
UPDATE path be taken must pass the (UPDATE or ALL) USING
qualifications (combined using OR), which are always enforced as
WITH CHECK options in this context. (The UPDATE path will never be
silently avoided; an error will be thrown instead.) Finally, the
final row appended to the relation must pass any WITH CHECK options
that a conventional UPDATE is required to pass.
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.
When a DELETE command is used with a WHERE clause or a RETURNING
clause, SELECT rights are also required on the relation being
updated and the appropriate SELECT and ALL policies will be
combined (using OR for any overlapping SELECT related policies
found) with the USING clause of the DELETE policy using AND.
Therefore, in order for a user to be able to DELETE specific rows,
the user must have access to the row(s) through a SELECT or ALL
policy and the row(s) must pass the DELETE policy's USING
expression.
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.
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, “Row Security Policies”, in the documentation.
COMPATIBILITY
CREATE POLICY is a PostgreSQL extension.
SEE ALSO
ALTER POLICY (ALTER_POLICY(7)), DROP POLICY (DROP_POLICY(7)), ALTER
TABLE (ALTER_TABLE(7))
PostgreSQL 9.5.0 2016 CREATE POLICY(7)
