Document that zero-column tables are allowed (and non-standard).

doc/src/sgml/ref/alter_table.sgml

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-$Header: /cvsroot/pgsql/doc/src/sgml/ref/alter_table.sgml,v 1.52 2002/10/19 23:09:20 tgl Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/alter_table.sgml,v 1.53 2002/12/16 19:08:25 tgl Exp $
 PostgreSQL documentation
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@@ -506,6 +506,12 @@ ALTER TABLE distributors ADD PRIMARY KEY (dist_id);
     The clauses to rename tables, columns, indexes, and sequences are
     <productname>PostgreSQL</productname> extensions from SQL92.
    </para>
+
+   <para>
+    <command>ALTER TABLE DROP COLUMN</> can be used to drop the only column
+    of a table, leaving a zero-column table.  This is an extension from SQL92,
+    which disallows zero-column tables.
+   </para>
  
   </refsect2>
  </refsect1>

doc/src/sgml/ref/create_table.sgml

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-$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_table.sgml,v 1.59 2002/11/21 23:34:43 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_table.sgml,v 1.60 2002/12/16 19:08:25 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -915,6 +915,19 @@ CREATE ASSERTION <replaceable>name</replaceable> CHECK ( <replaceable>condition<
     standard.
    </para>
   </refsect2>
+
+  <refsect2>
+   <title>Zero-column tables</title>
+
+   <para>
+    <productname>PostgreSQL</productname> allows a table of no columns
+    to be created (for example, <literal>CREATE TABLE foo();</>).  This
+    is an extension from the SQL standard, which does not allow zero-column
+    tables.  Zero-column tables are not in themselves very useful, but
+    disallowing them creates odd special cases for <command>ALTER TABLE
+    DROP COLUMN</>, so it seems cleaner to ignore this spec restriction.
+   </para>
+  </refsect2>
  </refsect1>