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$PostgreSQL: pgsql/doc/src/sgml/ref/grant.sgml,v 1.44.4.2 2008/05/28 00:46:05 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 | RULE | REFERENCES | TRIGGER }
    [,...] | ALL [ PRIVILEGES ] }
    ON [ TABLE ] <replaceable class="PARAMETER">tablename</replaceable> [, ...]
    TO { <replaceable class="PARAMETER">username</replaceable> | GROUP <replaceable class="PARAMETER">groupname</replaceable> | PUBLIC } [, ...] [ WITH GRANT OPTION ]

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

GRANT { EXECUTE | ALL [ PRIVILEGES ] }
    ON FUNCTION <replaceable>funcname</replaceable> ([<replaceable>type</replaceable>, ...]) [, ...]
    TO { <replaceable class="PARAMETER">username</replaceable> | GROUP <replaceable class="PARAMETER">groupname</replaceable> | PUBLIC } [, ...] [ WITH GRANT OPTION ]

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

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

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

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

  <para>
   The <command>GRANT</command> command gives specific privileges on
   an object (table, view, sequence, database, function,
   procedural language, schema, or tablespace) to
   one or more users or groups of users.  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 users, including those that may
   be created later.  <literal>PUBLIC</literal> may be thought of as an
   implicitly defined group that always includes all users.
   Any particular user will have the sum
   of privileges granted directly to him, privileges granted to any group he
   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 may in turn grant it to others.  Without a grant
   option, the recipient cannot do that.  At present, grant options can
   only be granted to individual users, not to groups or
   <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 may
   include granting some privileges to <literal>PUBLIC</literal>.
   The default is no public access for tables, schemas, and tablespaces;
   <literal>TEMP</> table creation privilege for databases;
   <literal>EXECUTE</> privilege for functions; and
   <literal>USAGE</> privilege for languages.
   The object owner may 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
   may 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>
       also requires 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>RULE</term>
     <listitem>
      <para>
       Allows the creation of a rule on the table/view.  (See the <xref
       linkend="sql-createrule" endterm="sql-createrule-title"> statement.)
      </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 and indexes 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>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.
      </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>
 </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.
   </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=arwdRxt/miriam,=r/miriam,"group todos=arw/miriam"}
(1 row)
</programlisting>
    The entries shown by <command>\z</command> are interpreted thus:
<programlisting>
              =xxxx -- privileges granted to PUBLIC
         uname=xxxx -- privileges granted to a user
   group gname=xxxx -- privileges granted to a group

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

              /yyyy -- user who 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 GROUP todos;
</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 may 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=arwdRxt/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>
 </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>
    The SQL standard allows setting privileges for individual columns
    within a table:

<synopsis>
GRANT <replaceable class="PARAMETER">privileges</replaceable>
    ON <replaceable class="PARAMETER">table</replaceable> [ ( <replaceable class="PARAMETER">column</replaceable> [, ...] ) ] [, ...]
    TO { PUBLIC | <replaceable class="PARAMETER">username</replaceable> [, ...] } [ WITH GRANT OPTION ]
</synopsis>
   </para>

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

   <para>
    The <literal>RULE</literal> privilege, and privileges on
    databases, tablespaces, schemas, languages, and sequences are
    <productname>PostgreSQL</productname> extensions.
   </para>
 </refsect1>


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

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

</refentry>

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