Specifies a <literal>DELETE</literal> action that deletes the current row
      of the target table.
      Do not include the table name or any other clauses, as you would normally
      do with a <xref linkend="sql-delete"/> command.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">column_name</replaceable></term>
    <listitem>
     <para>
      The name of a column in the target table.  The column name
      can be qualified with a subfield name or array subscript, if
      needed.  (Inserting into only some fields of a composite
      column leaves the other fields null.)
      Do not include the table's name in the specification
      of a target column.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>OVERRIDING SYSTEM VALUE</literal></term>
    <listitem>
     <para>
      Without this clause, it is an error to specify an explicit value
      (other than <literal>DEFAULT</literal>) for an identity column defined
      as <literal>GENERATED ALWAYS</literal>.  This clause overrides that
      restriction.
     </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 defined as <literal>GENERATED BY DEFAULT</literal> are ignored
      and the default sequence-generated values are applied.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>DEFAULT VALUES</literal></term>
    <listitem>
     <para>
      All columns will be filled with their default values.
      (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 to assign to the column.  If used in a
      <literal>WHEN MATCHED</literal> clause, the expression can use values
      from the original row in the target table, and values from the
      <replaceable class="parameter">data_source</replaceable> row.
      If used in a <literal>WHEN NOT MATCHED BY SOURCE</literal> clause, the
      expression can only use values from the original row in the target table.
      If used in a <literal>WHEN NOT MATCHED [BY TARGET]</literal> clause, the
      expression can only use values from the
      <replaceable class="parameter">data_source</replaceable> row.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>DEFAULT</literal></term>
    <listitem>
     <para>
      Set the column to its default value (which will be <literal>NULL</literal>
      if no specific default expression has been assigned to it).
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">sub-SELECT</replaceable></term>
    <listitem>
     <para>
      A <literal>SELECT</literal> sub-query that produces as many output columns
      as are listed in the parenthesized column list preceding it.  The
      sub-query must yield no more than one row when executed.  If it
      yields one row, its column values are assigned to the target columns;
      if it yields no rows, NULL values are assigned to the target columns.
      If used in a <literal>WHEN MATCHED</literal> clause, the sub-query can
      refer to values from the original row in the target table, and values
      from the <replaceable class="parameter">data_source</replaceable> row.
      If used in a <literal>WHEN NOT MATCHED BY SOURCE</literal> clause, the
      sub-query can only refer to values from the original row in the target
      table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">output_alias</replaceable></term>
    <listitem>
     <para>
      An optional substitute name for <literal>OLD</literal>