CREATE POLICY

Name

CREATE 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.

Compatibility

CREATE POLICY is a PostgreSQL extension.

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