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$PostgreSQL: pgsql/doc/src/sgml/ref/grant.sgml,v 1.71 2008/09/08 00:47:40 tgl Exp $
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<refentry id="SQL-GRANT">
 <refmeta>
  <refentrytitle id="sql-grant-title">GRANT</refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>GRANT</refname>
  <refpurpose>define access privileges</refpurpose>
 </refnamediv>

 <indexterm zone="sql-grant">
  <primary>GRANT</primary>
 </indexterm>

 <refsynopsisdiv>
<synopsis>
GRANT { { SELECT | INSERT | UPDATE | DELETE | TRUNCATE | REFERENCES | TRIGGER }
    [,...] | ALL [ PRIVILEGES ] }
    ON [ TABLE ] <replaceable class="PARAMETER">tablename</replaceable> [, ...]
    TO { [ GROUP ] <replaceable class="PARAMETER">rolename</replaceable> | PUBLIC } [, ...] [ WITH GRANT OPTION ]

GRANT { { USAGE | SELECT | UPDATE }
    [,...] | ALL [ PRIVILEGES ] }
    ON SEQUENCE <replaceable class="PARAMETER">sequencename</replaceable> [, ...]
    TO { [ GROUP ] <replaceable class="PARAMETER">rolename</replaceable> | PUBLIC } [, ...] [ WITH GRANT OPTION ]

GRANT { { CREATE | CONNECT | TEMPORARY | TEMP } [,...] | ALL [ PRIVILEGES ] }
    ON DATABASE <replaceable>dbname</replaceable> [, ...]
    TO { [ GROUP ] <replaceable class="PARAMETER">rolename</replaceable> | PUBLIC } [, ...] [ WITH GRANT OPTION ]

GRANT { EXECUTE | ALL [ PRIVILEGES ] }
    ON FUNCTION <replaceable>funcname</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) [, ...]
    TO { [ GROUP ] <replaceable class="PARAMETER">rolename</replaceable> | PUBLIC } [, ...] [ WITH GRANT OPTION ]

GRANT { USAGE | ALL [ PRIVILEGES ] }
    ON LANGUAGE <replaceable>langname</replaceable> [, ...]
    TO { [ GROUP ] <replaceable class="PARAMETER">rolename</replaceable> | PUBLIC } [, ...] [ WITH GRANT OPTION ]

GRANT { { CREATE | USAGE } [,...] | ALL [ PRIVILEGES ] }
    ON SCHEMA <replaceable>schemaname</replaceable> [, ...]
    TO { [ GROUP ] <replaceable class="PARAMETER">rolename</replaceable> | PUBLIC } [, ...] [ WITH GRANT OPTION ]

GRANT { CREATE | ALL [ PRIVILEGES ] }
    ON TABLESPACE <replaceable>tablespacename</> [, ...]
    TO { [ GROUP ] <replaceable class="PARAMETER">rolename</replaceable> | PUBLIC } [, ...] [ WITH GRANT OPTION ]

GRANT <replaceable class="PARAMETER">role</replaceable> [, ...] TO <replaceable class="PARAMETER">rolename</replaceable> [, ...] [ WITH ADMIN OPTION ]
</synopsis>
 </refsynopsisdiv>

 <refsect1 id="sql-grant-description">
  <title>Description</title>

  <para>
   The <command>GRANT</command> command has two basic variants: one
   that grants privileges on a database object (table, view, sequence,
   database, function, procedural language, schema, or tablespace),
   and one that grants membership in a role.  These variants are
   similar in many ways, but they are different enough to be described
   separately.
  </para>

  <para>
   As of <productname>PostgreSQL</productname> 8.1, the concepts of users and
   groups have been unified into a single kind of entity called a role.
   It is therefore no longer necessary to use the keyword <literal>GROUP</>
   to identify whether a grantee is a user or a group.  <literal>GROUP</>
   is still allowed in the command, but it is a noise word.
  </para>

 <refsect2 id="sql-grant-description-objects">
  <title>GRANT on Database Objects</title>

  <para>
   This variant of the <command>GRANT</command> command gives specific
   privileges on a database object to
   one or more roles.  These privileges are added
   to those already granted, if any.
  </para>

  <para>
   The key word <literal>PUBLIC</literal> indicates that the
   privileges are to be granted to all roles, including those that might
   be created later.  <literal>PUBLIC</literal> can be thought of as an
   implicitly defined group that always includes all roles.
   Any particular role will have the sum
   of privileges granted directly to it, privileges granted to any role it
   is presently a member of, and privileges granted to
   <literal>PUBLIC</literal>.
  </para>

  <para>
   If <literal>WITH GRANT OPTION</literal> is specified, the recipient
   of the privilege can in turn grant it to others.  Without a grant
   option, the recipient cannot do that.  Grant options cannot be granted
   to <literal>PUBLIC</literal>.
  </para>

  <para>
   There is no need to grant privileges to the owner of an object
   (usually the user that created it),
   as the owner has all privileges by default.  (The owner could,
   however, choose to revoke some of his own privileges for safety.)
   The right to drop an object, or to alter its definition in any way is
   not described by a grantable privilege; it is inherent in the owner,
   and cannot be granted or revoked.  The owner implicitly has all grant
   options for the object, too.
  </para>

  <para>
   Depending on the type of object, the initial default privileges might
   include granting some privileges to <literal>PUBLIC</literal>.
   The default is no public access for tables, schemas, and tablespaces;
   <literal>CONNECT</> privilege and <literal>TEMP</> table creation privilege
   for databases;
   <literal>EXECUTE</> privilege for functions; and
   <literal>USAGE</> privilege for languages.
   The object owner can of course revoke these privileges.  (For maximum
   security, issue the <command>REVOKE</> in the same transaction that
   creates the object; then there is no window in which another user
   can use the object.)
  </para>

  <para>
   The possible privileges are:

   <variablelist>
    <varlistentry>
     <term>SELECT</term>
     <listitem>
      <para>
       Allows <xref linkend="sql-select" endterm="sql-select-title"> from
       any column of the specified table, view, or sequence.
       Also allows the use of
       <xref linkend="sql-copy" endterm="sql-copy-title"> TO.
       This privilege is also needed to reference existing column values in
       <xref linkend="sql-update" endterm="sql-update-title"> or
       <xref linkend="sql-delete" endterm="sql-delete-title">.
       For sequences, this privilege also allows the use of the
       <function>currval</function> function.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>INSERT</term>
     <listitem>
      <para>
       Allows <xref linkend="sql-insert" endterm="sql-insert-title"> of a new
       row into the specified table.
       Also allows <xref linkend="sql-copy" endterm="sql-copy-title"> FROM.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>UPDATE</term>
     <listitem>
      <para>
       Allows <xref linkend="sql-update" endterm="sql-update-title"> of any
       column of the specified table.
       (In practice, any nontrivial <command>UPDATE</> command will require
       <literal>SELECT</> privilege as well, since it must reference table
       columns to determine which rows to update, and/or to compute new
       values for columns.)
       <literal>SELECT ... FOR UPDATE</literal>
       and <literal>SELECT ... FOR SHARE</literal>
       also require this privilege, in addition to the
       <literal>SELECT</literal> privilege.  For sequences, this
       privilege allows the use of the <function>nextval</function> and
       <function>setval</function> functions.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>DELETE</term>
     <listitem>
      <para>
       Allows <xref linkend="sql-delete" endterm="sql-delete-title"> of a row
       from the specified table.
       (In practice, any nontrivial <command>DELETE</> command will require
       <literal>SELECT</> privilege as well, since it must reference table
       columns to determine which rows to delete.)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>TRUNCATE</term>
     <listitem>
      <para>
       Allows <xref linkend="sql-truncate" endterm="sql-truncate-title"> on
       the specified table.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>REFERENCES</term>
     <listitem>
      <para>
       To create a foreign key constraint, it is
       necessary to have this privilege on both the referencing and
       referenced tables.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>TRIGGER</term>
     <listitem>
      <para>
       Allows the creation of a trigger on the specified table.  (See the
       <xref linkend="sql-createtrigger" endterm="sql-createtrigger-title"> statement.)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>CREATE</term>
     <listitem>
      <para>
       For databases, allows new schemas to be created within the database.
      </para>
      <para>
       For schemas, allows new objects to be created within the schema.
       To rename an existing object, you must own the object <emphasis>and</>
       have this privilege for the containing schema.
      </para>
      <para>
       For tablespaces, allows tables, indexes, and temporary files to be
       created within the tablespace, and allows databases to be created that
       have the tablespace as their default tablespace.  (Note that revoking
       this privilege will not alter the placement of existing objects.)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>CONNECT</term>
     <listitem>
      <para>
       Allows the user to connect to the specified database.  This
       privilege is checked at connection startup (in addition to checking
       any restrictions imposed by <filename>pg_hba.conf</>).
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>TEMPORARY</term>
     <term>TEMP</term>
     <listitem>
      <para>
       Allows temporary tables to be created while using the specified database.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>EXECUTE</term>
     <listitem>
      <para>
       Allows the use of the specified function and the use of any
       operators that are implemented on top of the function.  This is
       the only type of privilege that is applicable to functions.
       (This syntax works for aggregate functions, as well.)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>USAGE</term>
     <listitem>
      <para>
       For procedural languages, allows the use of the specified language for
       the creation of functions in that language.  This is the only type
       of privilege that is applicable to procedural languages.
      </para>
      <para>
       For schemas, allows access to objects contained in the specified
       schema (assuming that the objects' own privilege requirements are
       also met).  Essentially this allows the grantee to <quote>look up</>
       objects within the schema.  Without this permission, it is still
       possible to see the object names, e.g. by querying the system tables.
       Also, after revoking this permission, existing backends might have
       statements that have previously performed this lookup, so this is not
       a completely secure way to prevent object access.
      </para>
      <para>
       For sequences, this privilege allows the use of the
       <function>currval</function> and <function>nextval</function> functions.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>ALL PRIVILEGES</term>
     <listitem>
      <para>
       Grant all of the available privileges at once.
       The <literal>PRIVILEGES</literal> key word is optional in
       <productname>PostgreSQL</productname>, though it is required by
       strict SQL.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>

   The privileges required by other commands are listed on the
   reference page of the respective command.
  </para>
 </refsect2>

 <refsect2 id="sql-grant-description-roles">
  <title>GRANT on Roles</title>

  <para>
   This variant of the <command>GRANT</command> command grants membership
   in a role to one or more other roles.  Membership in a role is significant
   because it conveys the privileges granted to a role to each of its
   members.
  </para>

  <para>
   If <literal>WITH ADMIN OPTION</literal> is specified, the member can
   in turn grant membership in the role to others, and revoke membership
   in the role as well.  Without the admin option, ordinary users cannot do
   that.  However,
   database superusers can grant or revoke membership in any role to anyone.
   Roles having <literal>CREATEROLE</> privilege can grant or revoke
   membership in any role that is not a superuser.
  </para>

  <para>
   Unlike the case with privileges, membership in a role cannot be granted
   to <literal>PUBLIC</>.  Note also that this form of the command does not
   allow the noise word <literal>GROUP</>.
  </para>
 </refsect2>
 </refsect1>


 <refsect1 id="SQL-GRANT-notes">
  <title>Notes</title>

   <para>
    The <xref linkend="sql-revoke" endterm="sql-revoke-title"> command is used
    to revoke access privileges.
   </para>

   <para>
    When a non-owner of an object attempts to <command>GRANT</> privileges
    on the object, the command will fail outright if the user has no
    privileges whatsoever on the object.  As long as some privilege is
    available, the command will proceed, but it will grant only those
    privileges for which the user has grant options.  The <command>GRANT ALL
    PRIVILEGES</> forms will issue a warning message if no grant options are
    held, while the other forms will issue a warning if grant options for
    any of the privileges specifically named in the command are not held.
    (In principle these statements apply to the object owner as well, but
    since the owner is always treated as holding all grant options, the
    cases can never occur.)
   </para>

   <para>
    It should be noted that database superusers can access
    all objects regardless of object privilege settings.  This
    is comparable to the rights of <literal>root</> in a Unix system.
    As with <literal>root</>, it's unwise to operate as a superuser
    except when absolutely necessary.
   </para>

   <para>
    If a superuser chooses to issue a <command>GRANT</> or <command>REVOKE</>
    command, the command is performed as though it were issued by the
    owner of the affected object.  In particular, privileges granted via
    such a command will appear to have been granted by the object owner.
    (For role membership, the membership appears to have been granted
    by the containing role itself.)
   </para>

   <para>
    <command>GRANT</> and <command>REVOKE</> can also be done by a role
    that is not the owner of the affected object, but is a member of the role
    that owns the object, or is a member of a role that holds privileges
    <literal>WITH GRANT OPTION</literal> on the object.  In this case the
    privileges will be recorded as having been granted by the role that
    actually owns the object or holds the privileges
    <literal>WITH GRANT OPTION</literal>.  For example, if table
    <literal>t1</> is owned by role <literal>g1</>, of which role
    <literal>u1</> is a member, then <literal>u1</> can grant privileges
    on <literal>t1</> to <literal>u2</>, but those privileges will appear
    to have been granted directly by <literal>g1</>.  Any other member
    of role <literal>g1</> could revoke them later.
   </para>

   <para>
    If the role executing <command>GRANT</> holds the required privileges
    indirectly via more than one role membership path, it is unspecified
    which containing role will be recorded as having done the grant.  In such
    cases it is best practice to use <command>SET ROLE</> to become the
    specific role you want to do the <command>GRANT</> as.
   </para>

   <para>
    Granting permission on a table does not automatically extend 
    permissions to any sequences used by the table, including 
    sequences tied to <type>SERIAL</> columns.  Permissions on 
    sequence must be set separately.
   </para>

   <para>
    Currently, <productname>PostgreSQL</productname> does not support
    granting or revoking privileges for individual columns of a table.
    One possible workaround is to create a view having just the desired
    columns and then grant privileges to that view.
   </para>

   <para>
    Use <xref linkend="app-psql">'s <command>\z</command> command
    to obtain information about existing privileges, for example:
<programlisting>
=&gt; \z mytable
                Access privileges
 Schema |  Name   | Type  |  Access privileges   
--------+---------+-------+-----------------------
 public | mytable | table | miriam=arwdDxt/miriam
                          : =r/miriam
                          : admin=arw/miriam
(1 row)
</programlisting>
    The entries shown by <command>\z</command> are interpreted thus:
<programlisting>
      rolename=xxxx -- privileges granted to a role
              =xxxx -- privileges granted to PUBLIC

                  r -- SELECT ("read")
                  w -- UPDATE ("write")
                  a -- INSERT ("append")
                  d -- DELETE
                  D -- TRUNCATE
                  x -- REFERENCES
                  t -- TRIGGER
                  X -- EXECUTE
                  U -- USAGE
                  C -- CREATE
                  c -- CONNECT
                  T -- TEMPORARY
            arwdDxt -- ALL PRIVILEGES (for tables)
                  * -- grant option for preceding privilege

              /yyyy -- role that granted this privilege
</programlisting>

    The above example display would be seen by user <literal>miriam</> after
    creating table <literal>mytable</> and doing:

<programlisting>
GRANT SELECT ON mytable TO PUBLIC;
GRANT SELECT, UPDATE, INSERT ON mytable TO admin;
</programlisting>
   </para>

   <para>
    If the <quote>Access privileges</> column is empty for a given object,
    it means the object has default privileges (that is, its privileges column
    is null).  Default privileges always include all privileges for the owner,
    and can include some privileges for <literal>PUBLIC</> depending on the
    object type, as explained above.  The first <command>GRANT</> or
    <command>REVOKE</> on an object
    will instantiate the default privileges (producing, for example,
    <literal>{miriam=arwdDxt/miriam}</>) and then modify them per the
    specified request.
   </para>

   <para>
    Notice that the owner's implicit grant options are not marked in the
    access privileges display.  A <literal>*</> will appear only when
    grant options have been explicitly granted to someone.
   </para>
 </refsect1>

 <refsect1 id="sql-grant-examples">
  <title>Examples</title>

  <para>
   Grant insert privilege to all users on table <literal>films</literal>:

<programlisting>
GRANT INSERT ON films TO PUBLIC;
</programlisting>
  </para>

  <para>
   Grant all available privileges to user <literal>manuel</literal> on view
   <literal>kinds</literal>:

<programlisting>
GRANT ALL PRIVILEGES ON kinds TO manuel;
</programlisting>

   Note that while the above will indeed grant all privileges if executed by a
   superuser or the owner of <literal>kinds</literal>, when executed by someone
   else it will only grant those permissions for which the someone else has
   grant options.
  </para>

  <para>
   Grant membership in role <literal>admins</> to user <literal>joe</>:

<programlisting>
GRANT admins TO joe;
</programlisting>
  </para>
 </refsect1>

 <refsect1 id="sql-grant-compatibility">
  <title>Compatibility</title>

   <para>
    According to the SQL standard, the <literal>PRIVILEGES</literal>
    key word in <literal>ALL PRIVILEGES</literal> is required.  The
    SQL standard does not support setting the privileges on more than
    one object per command.
   </para>

   <para>
    <productname>PostgreSQL</productname> allows an object owner to revoke his
    own ordinary privileges: for example, a table owner can make the table
    read-only to himself by revoking his own <literal>INSERT</>,
    <literal>UPDATE</>, <literal>DELETE</>, and <literal>TRUNCATE</>
    privileges.  This is not possible according to the SQL standard.  The
    reason is that <productname>PostgreSQL</productname> treats the owner's
    privileges as having been granted by the owner to himself; therefore he
    can revoke them too.  In the SQL standard, the owner's privileges are
    granted by an assumed entity <quote>_SYSTEM</>.  Not being
    <quote>_SYSTEM</>, the owner cannot revoke these rights.
   </para>

   <para>
    <productname>PostgreSQL</productname> does not support the SQL-standard 
    functionality of setting privileges for individual columns.
   </para>

   <para>
    The SQL standard provides for a <literal>USAGE</literal> privilege
    on other kinds of objects: character sets, collations,
    translations, domains.
   </para>

   <para>
    Privileges on databases, tablespaces, schemas, and languages are
    <productname>PostgreSQL</productname> extensions.
   </para>
 </refsect1>


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

  <simpara>
   <xref linkend="sql-revoke" endterm="sql-revoke-title">
  </simpara>
 </refsect1>

</refentry>
