class Item_func_isnull :public Item_func_null_predicate

{

  ..

  bool arg_is_datetime_notnull_field()

  {

    Item **args= arguments();

    if (args[0]->real_item()->type() == Item::FIELD_ITEM)

    {

      Field *field=((Item_field*) args[0]->real_item())->field;

      if (((field->type() == MYSQL_TYPE_DATE) ||

          (field->type() == MYSQL_TYPE_DATETIME)) &&

          (field->flags & NOT_NULL_FLAG))

        return true;

    }

  ..

};

COND *

Item_func_isnull::remove_eq_conds(THD *thd, Item::cond_result *cond_value,

                                  bool top_level_arg)

{

 ..

   if (((field->type() == MYSQL_TYPE_DATE) ||

        (field->type() == MYSQL_TYPE_DATETIME)) &&

        (field->flags & NOT_NULL_FLAG))

  ..

}

  virtual bool cond_notnull_field_isnull_to_field_eq_zero() const

  {

    return false;

  }