CREATE POLICY(7)

NAME
CREATE_POLICY - define a new 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 policy for a table. Note that row-level security must also be enabled on the table using ALTER TABLE 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 via USING, while new rows that would be created via INSERT or UPDATE are checked against the expression specified via WITH CHECK. When a USING expression returns true for a given row then that row is visible to the user, while if a 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 added, while if a false or null is returned then an error occurs.

Generally, the system will enforce filter conditions imposed using security policies prior to qualifications that appear in the query itself, in order to prevent the 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.

For INSERT and UPDATE statements, WITH CHECK expressions are enforced after BEFORE triggers are fired, and before any 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).

Further, 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 for both what rows are visible (normal USING case) and which rows will be allowed to be added (WITH CHECK case).

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 roles 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 and 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.

check_expression
    Any SQL conditional expression (returning boolean). The conditional expression cannot contain any aggregate or window functions. This expression will be used with INSERT and UPDATE queries against the table if row level security is enabled and only rows where 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.

  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 policy for both if only a USING policy has been defined.

    As an example, if an UPDATE is issued, then the ALL policy will be applicable to both what the UPDATE will be able to select out as rows to be updated (with the USING expression being applied), and it will be applied to rows that result from the UPDATE statement, to check if they are permitted to be added to the table (using 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 WITH CHECK expression, the entire command will be aborted. Note that if only a USING clause is specified then that clause will be used for both USING and WITH CHECK cases.

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, even if other records exist in the relation and that queries which require SELECT permissions, such as UPDATE, will also only see those records which are allowed by the SELECT policy. The SELECT policy only accepts the USING 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. The INSERT policy only accepts the WITH CHECK expression as it only applies in cases where records are being added to the relation.

    Note that INSERT with ON CONFLICT DO UPDATE requires that any INSERT policy WITH CHECK expression passes for any rows appended to the relation by the INSERT path only.

UPDATE
    Using UPDATE for a policy means that it will apply to UPDATE commands (or auxiliary ON CONFLICT DO UPDATE clauses of INSERT commands). As UPDATE involves pulling an existing record and then making changes to some portion (but possibly not all) of the record, the UPDATE policy accepts both a USING expression and a WITH CHECK expression.

    The USING expression will be used to determine which records the UPDATE command will see to operate against, while the WITH CHECK expression defines what rows are allowed to be added back into the relation (similar to the INSERT policy).

    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 a specific set of rows using a WHERE clause, the user must have access to the row(s) through a SELECT or ALL policy and the row(s) must be pass the UPDATE USING expression.

    Any rows whose resulting 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 seen by a DELETE, if they do not pass the USING expression for the DELETE.

    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 a specific set of rows using a WHERE clause, the user must have access to the row(s) through a SELECT or ALL policy and the row(s) must be pass the DELETE USING expression.

    The DELETE policy only accepts the USING expression as it only applies in cases where records are being extracted from the relation for deletion.

NOTES

You must be the owner of a table to create or change policies for it.

Note that while policies will be applied for explicit queries against tables in the system, 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 which is the 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 that 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.

Regarding how policy expressions interact with the user: as the 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.

When reducing the set of rows which a user has access to, through modifications to relations referenced by Row-Level Security Policies or Security Barrier Views, be aware that users with a currently open transaction may be able to see updates to the rows that they are no longer allowed access. Therefore, the best practice to avoid any possible leak of information when altering conditions that determine the visibility of specific rows is to ensure that affected users do not have any open transactions, perhaps by ensuring they have no concurrent sessions running.

COMPATIBILITY

CREATE POLICY is a PostgreSQL extension.

SEE ALSO
ALTER POLICY (ALTER_POLICY(7)), DROP POLICY (DROP_POLICY(7))