fields null.)  When referencing a
        column with <literal>ON CONFLICT DO UPDATE</literal>, do not include
        the table's name in the specification of a target column.  For
        example, <literal>INSERT INTO table_name ... ON CONFLICT DO UPDATE
        SET table_name.col = 1</literal> is invalid (this follows the general
        behavior for <command>UPDATE</command>).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>OVERRIDING SYSTEM VALUE</literal></term>
      <listitem>
       <para>
        If this clause is specified, then any values supplied for identity
        columns will override the default sequence-generated values.
       </para>

       <para>
        For an identity column defined as <literal>GENERATED ALWAYS</literal>,
        it is an error to insert an explicit value (other than
        <literal>DEFAULT</literal>) without specifying either
        <literal>OVERRIDING SYSTEM VALUE</literal> or <literal>OVERRIDING USER
        VALUE</literal>.  (For an identity column defined as
        <literal>GENERATED BY DEFAULT</literal>, <literal>OVERRIDING SYSTEM
        VALUE</literal> is the normal behavior and specifying it does nothing,
        but <productname>PostgreSQL</productname> allows it as an extension.)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>OVERRIDING USER VALUE</literal></term>
      <listitem>
       <para>
        If this clause is specified, then any values supplied for identity
        columns are ignored and the default sequence-generated values are
        applied.
       </para>

       <para>
        This clause is useful for example when copying values between tables.
        Writing <literal>INSERT INTO tbl2 OVERRIDING USER VALUE SELECT * FROM
        tbl1</literal> will copy from <literal>tbl1</literal> all columns that
        are not identity columns in <literal>tbl2</literal> while values for
        the identity columns in <literal>tbl2</literal> will be generated by
        the sequences associated with <literal>tbl2</literal>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>DEFAULT VALUES</literal></term>
      <listitem>
       <para>
        All columns will be filled with their default values, as if
        <literal>DEFAULT</literal> were explicitly specified for each column.
        (An <literal>OVERRIDING</literal> clause is not permitted in this
        form.)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">expression</replaceable></term>
      <listitem>
       <para>
        An expression or value to assign to the corresponding column.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>DEFAULT</literal></term>
      <listitem>
       <para>
        The corresponding column will be filled with its default value.  An
        identity column will be filled with a new value generated by the
        associated sequence.  For a generated column, specifying this is
        permitted but merely specifies the normal behavior of computing the
        column from its generation expression.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">query</replaceable></term>
      <listitem>
       <para>
        A query (<command>SELECT</command> statement) that supplies the
        rows to be inserted.  Refer to the
        <xref linkend="sql-select"/>
        statement for a description of the syntax.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">output_alias</replaceable></term>
      <listitem>
       <para>
        An optional substitute name for <literal>OLD</literal> or
        <literal>NEW</literal> rows in the <literal>RETURNING</literal> list.
       </para>

       <para>