grant.sgml

postgresql8.3.4源码,开源数据库

       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 for database "lusitania"
 Schema |  Name   | Type  |                 Access privileges                 
--------+---------+-------+---------------------------------------------------
 public | mytable | table | {miriam=arwdxt/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
                  x -- REFERENCES
                  t -- TRIGGER
                  X -- EXECUTE
                  U -- USAGE
                  C -- CREATE
                  c -- CONNECT
                  T -- TEMPORARY
             arwdxt -- 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=arwdxt/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 INSERT, UPDATE, and DELETE
    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>