PostgreSQL 9.5alpha1 Documentation
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# CREATE POLICY

## 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 ability to SELECT, INSERT, UPDATE, or DELETE rows which 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 the 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 queries, 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 query, 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 which 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).

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 which 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 RLS-enabled table. 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.

## 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 which 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 which 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 which 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` commands. The result is that only those records from the relation which pass the `SELECT` policy will be returned, even if other records exist in the relation. The `SELECT` policy only accepts the USING expression as it only ever 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 which 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 ever 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). Any rows whose resulting values do not pass the `WITH CHECK` expression will cause an ERROR and 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.

  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 WTIH 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 which pass this policy will be seen by a `DELETE` command. Rows may be visible through a `SELECT` which are not seen by a `DELETE`, as they do not pass the USING expression for the `DELETE`, and rows which are not visible through the `SELECT` policy may be deleted if they pass the `DELETE` USING policy. The `DELETE` policy only accepts the USING expression as it only ever 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.

In order to maintain referential integrity between two related tables, policies are not applied when the system performs checks on foreign key constraints.

## Compatibility

`CREATE POLICY` is a PostgreSQL extension.

## See Also

ALTER POLICY, DROP POLICY

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