candidate to update.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   <para>
    Note that exclusion constraints are not supported as arbiters with
    <literal>ON CONFLICT DO UPDATE</literal>. In all cases, only
    <literal>NOT DEFERRABLE</literal> constraints and unique indexes
    are supported as arbiters.
   </para>

   <para>
    <command>INSERT</command> with an <literal>ON CONFLICT DO UPDATE</literal>
    clause is a <quote>deterministic</quote> statement.  This means
    that the command will not be allowed to affect any single existing
    row more than once; a cardinality violation error will be raised
    when this situation arises.  Rows proposed for insertion should
    not duplicate each other in terms of attributes constrained by an
    arbiter index or constraint.
   </para>

   <para>
    Note that it is currently not supported for the
    <literal>ON CONFLICT DO UPDATE</literal> clause of an
    <command>INSERT</command> applied to a partitioned table to update the
    partition key of a conflicting row such that it requires the row be moved
    to a new partition.
   </para>
   <tip>
    <para>
     It is often preferable to use unique index inference rather than
     naming a constraint directly using <literal>ON CONFLICT ON
     CONSTRAINT</literal> <replaceable class="parameter">
     constraint_name</replaceable>.  Inference will continue to work
     correctly when the underlying index is replaced by another more
     or less equivalent index in an overlapping way, for example when
     using <literal>CREATE UNIQUE INDEX ...  CONCURRENTLY</literal>
     before dropping the index being replaced.
    </para>
   </tip>

  </refsect2>
 </refsect1>

 <refsect1>
  <title>Outputs</title>

  <para>
   On successful completion, an <command>INSERT</command> command returns a command
   tag of the form
<screen>
INSERT <replaceable>oid</replaceable> <replaceable class="parameter">count</replaceable>
</screen>
   The <replaceable class="parameter">count</replaceable> is the number of
   rows inserted or updated.  <replaceable>oid</replaceable> is always 0 (it
   used to be the <acronym>OID</acronym> assigned to the inserted row if
   <replaceable>count</replaceable> was exactly one and the target table was
   declared <literal>WITH OIDS</literal> and 0 otherwise, but creating a table
   <literal>WITH OIDS</literal> is not supported anymore).
  </para>

  <para>
   If the <command>INSERT</command> command contains a <literal>RETURNING</literal>
   clause, the result will be similar to that of a <command>SELECT</command>
   statement containing the columns and values defined in the
   <literal>RETURNING</literal> list, computed over the row(s) inserted or
   updated by the command.
  </para>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   If the specified table is a partitioned table, each row is routed to
   the appropriate partition and inserted into it.  If the specified table
   is a partition, an error will occur if one of the input rows violates
   the partition constraint.
  </para>

  <para>
   You may also wish to consider using <command>MERGE</command>, since that
   allows mixing <command>INSERT</command>, <command>UPDATE</command>, and
   <command>DELETE</command> within a single statement.
   See <xref linkend="sql-merge"/>.
  </para>
 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   Insert a single row into table <literal>films</literal>:

<programlisting>
INSERT INTO films VALUES
    ('UA502', 'Bananas', 105, '1971-07-13', 'Comedy', '82 minutes');
</programlisting>
  </para>

  <para>
   In this example, the <literal>len</literal> column is
   omitted and therefore it will have the default value:

<programlisting>
INSERT INTO films (code, title, did, date_prod, kind)
    VALUES ('T_601', 'Yojimbo', 106, '1961-06-16', 'Drama');
</programlisting>
  </para>

  <para>
   This example uses the <literal>DEFAULT</literal> clause for
   the date columns