double Item_std_field::val_real()
{
  double nr;
  // fix_fields() never calls for this Item
  nr= Item_variance_field::val_real();
  DBUG_ASSERT(nr >= 0.0);
  return sqrt(nr);
}
double Item_std_field::val_real()
{
  double nr;
   
  nr= Item_variance_field::val_real();
  DBUG_ASSERT(nr >= 0.0);
  return sqrt(nr);
}