Improve GRANT documentation to point out that UPDATE and DELETE typically

require SELECT privilege as well, since you normally need to read existing
column values within such commands.  This behavior is according to spec,
but we'd never documented it before.  Per gripe from Volkan Yazici.

doc/src/sgml/ref/grant.sgml

 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/grant.sgml,v 1.68 2008/05/05 01:21:03 adunstan Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/grant.sgml,v 1.69 2008/05/28 00:45:40 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -135,10 +135,15 @@ GRANT <replaceable class="PARAMETER">role</replaceable> [, ...] TO <replaceable
      <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.  For sequences, this
-       privilege also allows the use of the <function>currval</function> function.
+       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>
@@ -147,8 +152,9 @@ GRANT <replaceable class="PARAMETER">role</replaceable> [, ...] TO <replaceable
      <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.
+       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>
@@ -158,10 +164,15 @@ GRANT <replaceable class="PARAMETER">role</replaceable> [, ...] TO <replaceable
      <listitem>
       <para>
        Allows <xref linkend="sql-update" endterm="sql-update-title"> of any
-       column of the specified table.  <literal>SELECT ... FOR UPDATE</literal>
+       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 (besides the
-       <literal>SELECT</literal> privilege).  For sequences, this
+       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>
@@ -172,8 +183,11 @@ GRANT <replaceable class="PARAMETER">role</replaceable> [, ...] TO <replaceable
      <term>DELETE</term>
      <listitem>
       <para>
-       Allows <xref linkend="sql-delete" endterm="sql-delete-title"> of a row from the
-       specified table.
+       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>
@@ -235,7 +249,7 @@ GRANT <replaceable class="PARAMETER">role</replaceable> [, ...] TO <replaceable
      <term>TEMP</term>
      <listitem>
       <para>
-       Allows temporary tables to be created while using the database.
+       Allows temporary tables to be created while using the specified database.
       </para>
      </listitem>
     </varlistentry>