CREATE POLICY
CREATE POLICY — define a new row level security policy for a table
Synopsis
CREATE POLICYname
ONtable_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. Multiple policies may apply to a single command; see below for more details. Table 222 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.
command
The command to which the policy applies. Valid options are
ALL
,SELECT
,INSERT
,UPDATE
, andDELETE
.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 aSELECT
), and will not be available for modification (in anUPDATE
orDELETE
). 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 inINSERT
andUPDATE
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 thecheck_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 anALL
policy exists and more specific policies exist, then both theALL
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 theUSING
expression for both cases if only aUSING
expression has been defined.As an example, if an
UPDATE
is issued, then theALL
policy will be applicable both to what theUPDATE
will be able to select as rows to be updated (applying theUSING
expression), and to the resulting updated rows, to check if they are permitted to be added to the table (applying theWITH CHECK
expression, if defined, and theUSING
expression otherwise). If anINSERT
orUPDATE
command attempts to add rows to the table that do not pass theALL
policy'sWITH CHECK
expression, the entire command will be aborted.SELECT
Using
SELECT
for a policy means that it will apply toSELECT
queries and wheneverSELECT
permissions are required on the relation the policy is defined for. The result is that only those records from the relation that pass theSELECT
policy will be returned during aSELECT
query, and that queries that requireSELECT
permissions, such asUPDATE
, will also only see those records that are allowed by theSELECT
policy. ASELECT
policy cannot have aWITH 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 toINSERT
commands. Rows being inserted that do not pass this policy will result in a policy violation error, and the entireINSERT
command will be aborted. AnINSERT
policy cannot have aUSING
expression, as it only applies in cases where records are being added to the relation.Note that
INSERT
withON CONFLICT DO UPDATE
checksINSERT
policies'WITH CHECK
expressions only for rows appended to the relation by theINSERT
path.UPDATE
Using
UPDATE
for a policy means that it will apply toUPDATE
,SELECT FOR UPDATE
andSELECT FOR SHARE
commands, as well as auxiliaryON CONFLICT DO UPDATE
clauses ofINSERT
commands. SinceUPDATE
involves pulling an existing record and replacing it with a new modified record,UPDATE
policies accept both aUSING
expression and aWITH CHECK
expression. TheUSING
expression determines which records theUPDATE
command will see to operate against, while theWITH 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 aUSING
clause is specified, then that clause will be used for bothUSING
andWITH CHECK
cases.Typically an
UPDATE
command also needs to read data from columns in the relation being updated (e.g., in aWHERE
clause or aRETURNING
clause, or in an expression on the right hand side of theSET
clause). In this case,SELECT
rights are also required on the relation being updated, and the appropriateSELECT
orALL
policies will be applied in addition to theUPDATE
policies. Thus the user must have access to the row(s) being updated through aSELECT
orALL
policy in addition to being granted permission to update the row(s) via anUPDATE
orALL
policy.When an
INSERT
command has an auxiliaryON CONFLICT DO UPDATE
clause, if theUPDATE
path is taken, the row to be updated is first checked against theUSING
expressions of anyUPDATE
policies, and then the new updated row is checked against theWITH CHECK
expressions. Note, however, that unlike a standaloneUPDATE
command, if the existing row does not pass theUSING
expressions, an error will be thrown (theUPDATE
path will never be silently avoided).DELETE
Using
DELETE
for a policy means that it will apply toDELETE
commands. Only rows that pass this policy will be seen by aDELETE
command. There can be rows that are visible through aSELECT
that are not available for deletion, if they do not pass theUSING
expression for theDELETE
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 aWHERE
clause or aRETURNING
clause). In this case,SELECT
rights are also required on the relation, and the appropriateSELECT
orALL
policies will be applied in addition to theDELETE
policies. Thus the user must have access to the row(s) being deleted through aSELECT
orALL
policy in addition to being granted permission to delete the row(s) via aDELETE
orALL
policy.A
DELETE
policy cannot have aWITH 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 222. Policies Applied by Command Type
Command | SELECT/ALL policy | INSERT/ALL policy | UPDATE/ALL policy | DELETE/ALL policy | |
---|---|---|---|---|---|
USING expression | WITH CHECK expression | USING expression | WITH CHECK expression | USING expression | |
SELECT | Existing row | — | — | — | — |
SELECT FOR UPDATE/SHARE | Existing row | — | Existing row | — | — |
INSERT | — | New row | — | — | — |
INSERT ... RETURNING | New row [a] | New row | — | — | — |
UPDATE | Existing & new rows [a] | — | Existing row | New row | — |
DELETE | Existing row [a] | — | — | — | Existing row |
ON CONFLICT DO UPDATE | Existing & new rows | — | Existing row | New row | — |
[a] If read access is required to the existing or new row (for example, a |
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 at least one of the policies must grant access to the relation. Thus the expressions from all the policies of that type are combined using the OR
operator. If there are no applicable 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 SELECT/ALL policy 1 ORexpression
from SELECT/ALL policy 2 OR ... ) AND (expression
from UPDATE/ALL policy 1 ORexpression
from 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.