path: root/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 row-security 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 } [, ...] ]
    [ USING ( <replaceable class="parameter">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 row-security
   policy for a table.  Note that row-security must also be enabled on the
   table using <command>ALTER TABLE</command> in order for created policies
   to be applied.
  </para>

  <para>
   A row-security policy is an expression which is added to the security-barrier
   qualifications of queries which are run against the table the policy is on,
   or an expression which is added to the with-check options for a table and
   which is applied to rows which would be added to the table.
   The security-barrier qualifications will always be evaluated prior to any
   user-defined functions or user-provided WHERE clauses, while the with-check
   expression will be evaluated against the rows which are going to be added to
   the table.  By adding policies to a table, a user can limit the rows which a
   given user can select, insert, update, or delete.  This capability is also
   known as Row-Level Security or RLS.
  </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.
  </para>

  <para>
   Note that while row-security 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">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 to filter out the records which are visible to the query.
     </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 condition expression cannot contain
      any aggregate or window functions.  This expression will be added
      to queries which are attempting to add records to the table as
      with-check options, and an error will be thrown if this condition
      returns false for any records being added.
     </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
         (or USING, if no WITH CHECK expression is defined) expression, the
         command will error.
       </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>
      </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.  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 USING expression and
         a WITH CHECK expression.  The USING 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.
       </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, row-security 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>