postgres/doc/src/sgml/ref/create_policy.sgml

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doc/src/sgml/ref/create_policy.sgml
PostgreSQL documentation
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<refentry id="SQL-CREATEPOLICY">
 <indexterm zone="sql-createpolicy">
  <primary>CREATE POLICY</primary>
 </indexterm>

 <refmeta>
  <refentrytitle>CREATE POLICY</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>CREATE POLICY</refname>
  <refpurpose>define a new policy for a table</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable class="parameter">table_name</replaceable>
    [ FOR { ALL | SELECT | INSERT | UPDATE | DELETE } ]
    [ TO { <replaceable class="parameter">role_name</replaceable> | PUBLIC | CURRENT_USER | SESSION_USER } [, ...] ]
    [ USING ( <replaceable class="parameter">using_expression</replaceable> ) ]
    [ WITH CHECK ( <replaceable class="parameter">check_expression</replaceable> ) ]
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   The <command>CREATE POLICY</command> command defines a new policy for a
   table.  Note that row level security must also be enabled on the table using
   <command>ALTER TABLE</command> in order for created policies to be applied.
  </para>

  <para>
   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.
  </para>

  <para>
   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.
  </para>

  <para>
    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.
  </para>

  <para>
   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.
  </para>

  <para>
   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 <literal>ON CONFLICT DO
   UPDATE</> and <literal>INSERT</> policies are not combined in this way, but
   rather enforced as noted at each stage of <literal>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).
  </para>

  <para>
   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.
  </para>

  <para>
   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.
  </para>

 </refsect1>

 <refsect1>
  <title>Parameters</title>

  <variablelist>
   <varlistentry>
    <term><replaceable class="parameter">name</replaceable></term>
    <listitem>
     <para>
      The name of the policy to be created.  This must be distinct from the
      name of any other policy for the table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">table_name</replaceable></term>
    <listitem>
     <para>
      The name (optionally schema-qualified) of the table the
      policy applies to.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">command</replaceable></term>
    <listitem>
     <para>
      The command to which the policy applies.  Valid options are
      <command>ALL</command>, <command>SELECT</command>,
      <command>INSERT</command>, <command>UPDATE</command>,
      and <command>DELETE</command>.
      <command>ALL</command> is the default.
      See below for specifics regarding how these are applied.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">role_name</replaceable></term>
    <listitem>
     <para>
      The roles to which the policy is to be applied.  The default is
      <literal>PUBLIC</literal>, which will apply the policy to all roles.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">using_expression</replaceable></term>
    <listitem>
     <para>
      Any <acronym>SQL</acronym> conditional expression (returning
      <type>boolean</type>).  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.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">check_expression</replaceable></term>
    <listitem>
     <para>
      Any <acronym>SQL</acronym> conditional expression (returning
      <type>boolean</type>).  The conditional expression cannot contain
      any aggregate or window functions.  This expression will be used with
      <command>INSERT</command> and <command>UPDATE</command> 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.
     </para>
    </listitem>
   </varlistentry>

  </variablelist>
 </refsect1>

 <refsect1>
   <title>Per-Command policies</title>

   <variablelist>

     <varlistentry id="SQL-CREATEPOLICY-ALL">
      <term><literal>ALL</></term>
      <listitem>
       <para>
         Using <literal>ALL</literal> for a policy means that it will apply
         to all commands, regardless of the type of command.  If an
         <literal>ALL</literal> policy exists and more specific policies
         exist, then both the <literal>ALL</literal> policy and the more
         specific policy (or policies) will be combined using
         <literal>OR</literal>, as usual for overlapping policies.
         Additionally, <literal>ALL</literal> 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 <literal>UPDATE</literal> is issued, then the
         <literal>ALL</literal> policy will be applicable to both what the
         <literal>UPDATE</literal> 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 <literal>UPDATE</literal>
         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 <literal>ALL</literal> WITH CHECK
         expression, the entire command will be aborted.  Note that if only a
         <literal>USING</literal> clause is specified then that clause will be
         used for both <literal>USING</literal> and
         <literal>WITH CHECK</literal> cases.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="SQL-CREATEPOLICY-SELECT">
      <term><literal>SELECT</></term>
      <listitem>
       <para>
         Using <literal>SELECT</literal> for a policy means that it will apply
         to <literal>SELECT</literal> commands.  The result is that only those
         records from the relation which pass the <literal>SELECT</literal>
         policy will be returned, even if other records exist in the relation.
         The <literal>SELECT</literal> policy only accepts the USING expression
         as it only ever applies in cases where records are being retrieved from
         the relation.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="SQL-CREATEPOLICY-INSERT">
      <term><literal>INSERT</></term>
      <listitem>
       <para>
         Using <literal>INSERT</literal> for a policy means that it will apply
         to <literal>INSERT</literal> commands.  Rows being inserted which do
         not pass this policy will result in a policy violation ERROR and the
         entire <literal>INSERT</literal> command will be aborted.  The
         <literal>INSERT</literal> policy only accepts the WITH CHECK expression
         as it only ever applies in cases where records are being added to the
         relation.
       </para>
       <para>
         Note that <literal>INSERT</literal> with <literal>ON CONFLICT DO
         UPDATE</literal> requires that any <literal>INSERT</literal> policy
         WITH CHECK expression passes for any rows appended to the relation by
         the INSERT path only.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="SQL-CREATEPOLICY-UPDATE">
      <term><literal>UPDATE</></term>
      <listitem>
       <para>
         Using <literal>UPDATE</literal> for a policy means that it will apply
         to <literal>UPDATE</literal> commands (or auxiliary <literal>ON
         CONFLICT DO UPDATE</literal> clauses of <literal>INSERT</literal>
         commands).  As <literal>UPDATE</literal> involves pulling an existing
         record and then making changes to some portion (but possibly not all)
         of the record, the <literal>UPDATE</literal> policy accepts both a
         <literal>USING</literal> expression and a <literal>WITH CHECK</literal>
         expression.  The <literal>USING</literal> expression will be used to
         determine which records the <literal>UPDATE</literal> command will see
         to operate against, while the <literal>WITH CHECK</literal> expression
         defines what rows are allowed to be added back into the relation
         (similar to the <literal>INSERT</literal> policy).  Any rows whose
         resulting values do not pass the <literal>WITH CHECK</literal>
         expression will cause an ERROR and the entire command will be aborted.
         Note that if only a <literal>USING</literal> clause is specified then
         that clause will be used for both <literal>USING</literal> and
         <literal>WITH CHECK</literal> cases.
       </para>
       <para>
         Note, however, that <literal>INSERT</literal> with <literal>ON CONFLICT
         DO UPDATE</literal> requires that an <literal>UPDATE</literal> policy
         <literal>USING</literal> expression always be enforced as a
         <literal>WITH CHECK</literal> expression.  This
         <literal>UPDATE</literal> policy must always pass when the
         <literal>UPDATE</literal> path is taken.  Any existing row that
         necessitates that the <literal>UPDATE</literal> path be taken must pass
         the (UPDATE or ALL) <literal>USING</literal> qualifications (combined
         using <literal>OR</literal>), which are always enforced as WTIH CHECK
         options in this context (the <literal>UPDATE</literal> path will
         <emphasis>never</> be silently avoided; an error will be thrown
         instead).  Finally, the final row appended to the relation must pass
         any <literal>WITH CHECK</literal> options that a conventional
         <literal>UPDATE</literal> is required to pass.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="SQL-CREATEPOLICY-DELETE">
      <term><literal>DELETE</></term>
      <listitem>
       <para>
         Using <literal>DELETE</literal> for a policy means that it will apply
         to <literal>DELETE</literal> commands.  Only rows which pass this
         policy will be seen by a <literal>DELETE</literal> command.  Rows may
         be visible through a <literal>SELECT</literal> which are not seen by a
         <literal>DELETE</literal>, as they do not pass the USING expression
         for the <literal>DELETE</literal>, and rows which are not visible
         through the <literal>SELECT</literal> policy may be deleted if they
         pass the <literal>DELETE</literal> USING policy.  The
         <literal>DELETE</literal> policy only accepts the USING expression as
         it only ever applies in cases where records are being extracted from
         the relation for deletion.
       </para>
      </listitem>
     </varlistentry>

   </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>

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

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

 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   <command>CREATE POLICY</command> is a <productname>PostgreSQL</productname>
   extension.
  </para>
 </refsect1>

 <refsect1>
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-alterpolicy"></member>
   <member><xref linkend="sql-droppolicy"></member>
  </simplelist>
 </refsect1>

</refentry>