Cleanup/remove/update references to OID column

Cleanup/remove/update references to OID column...

..in wake of 578b229718e8f.

See also
93507e67c9ca54026019ebec3026de35d30370f9
1464755fc490a9911214817fe83077a3689250ab
---
 doc/src/sgml/ddl.sgml          |  9 ++++-----
 doc/src/sgml/ref/insert.sgml   | 12 +++++-------
 doc/src/sgml/ref/psql-ref.sgml |  3 +++
 3 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index 9e761db..db044c5 100644
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -3672,11 +3672,10 @@ VALUES ('Albany', NULL, NULL, 'NY');
       <para>
        Partitions cannot have columns that are not present in the parent.  It
        is not possible to specify columns when creating partitions with
-       <command>CREATE TABLE</command>, nor is it possible to add columns to
-       partitions after-the-fact using <command>ALTER TABLE</command>.  Tables may be
-       added as a partition with <command>ALTER TABLE ... ATTACH PARTITION</command>
-       only if their columns exactly match the parent, including any
-       <literal>oid</literal> column.
+       <command>CREATE TABLE</command>, to add columns to
+       partitions after-the-fact using <command>ALTER TABLE</command>, nor to
+       add a partition with <command>ALTER TABLE ... ATTACH PARTITION</command>
+       if its columns would not exactly match those of the parent.
       </para>
      </listitem>
 
diff --git a/doc/src/sgml/ref/insert.sgml b/doc/src/sgml/ref/insert.sgml
index 62e142f..3e1be4c 100644
--- a/doc/src/sgml/ref/insert.sgml
+++ b/doc/src/sgml/ref/insert.sgml
@@ -552,13 +552,11 @@ INSERT INTO <replaceable class="parameter">table_name</replaceable> [ AS <replac
 INSERT <replaceable>oid</replaceable> <replaceable class="parameter">count</replaceable>
 </screen>
    The <replaceable class="parameter">count</replaceable> is the
-   number of rows inserted or updated.  If <replaceable
-   class="parameter">count</replaceable> is exactly one, and the
-   target table has OIDs, then <replaceable
-   class="parameter">oid</replaceable> is the <acronym>OID</acronym>
-   assigned to the inserted row.  The single row must have been
-   inserted rather than updated.  Otherwise <replaceable
-   class="parameter">oid</replaceable> is zero.
+   number of rows inserted or updated.
+   <replaceable>oid</replaceable> used to be the object ID of the inserted row
+   if <replaceable>rows</replaceable> was 1 and the target table had OIDs, but
+   OIDs system columns are not supported anymore; therefore
+   <replaceable>oid</replaceable> is always 0.
   </para>
 
   <para>
diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index 08f4bab..0e6e792 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -3794,6 +3794,9 @@ bar
         command. This variable is only guaranteed to be valid until
         after the result of the next <acronym>SQL</acronym> command has
         been displayed.
+        <productname>PostgreSQL</productname> servers since version 12 do not
+        support OID system columns in user tables, and LASTOID will always be 0
+        following <command>INSERT</command>.
         </para>
         </listitem>
       </varlistentry>
-- 
2.1.4