calc_group_buffer(JOIN *join,ORDER *group)
{
  uint key_length=0, parts=0, null_parts=0;

  if (group)
    join->group= 1;
  for (; group ; group=group->next)
  {
    Item *group_item= *group->item;
    Field *field= group_item->get_tmp_table_field();
    if (field)
    {
      enum_field_types type;
      if ((type= field->type()) == MYSQL_TYPE_BLOB)
	key_length+=MAX_BLOB_WIDTH;		// Can't be used as a key
      else if (type == MYSQL_TYPE_VARCHAR || type == MYSQL_TYPE_VAR_STRING)
        key_length+= field->field_length + HA_KEY_BLOB_LENGTH;
      else if (type == MYSQL_TYPE_BIT)
      {
        /* Bit is usually stored as a longlong key for group fields */
        key_length+= 8;                         // Big enough
      }
      else
	key_length+= field->pack_length();
    }
    else
    { 
      switch (group_item->cmp_type()) {
      case REAL_RESULT:
        key_length+= sizeof(double);
        break;
      case INT_RESULT:
        key_length+= sizeof(longlong);
        break;
      case DECIMAL_RESULT:
        key_length+= my_decimal_get_binary_size(group_item->max_length - 
                                                (group_item->decimals ? 1 : 0),
                                                group_item->decimals);
        break;
      case TIME_RESULT:
      {
        /*
          As items represented as DATE/TIME fields in the group buffer
          have STRING_RESULT result type, we increase the length 
          by 8 as maximum pack length of such fields.
        */
        key_length+= 8;
        break;
      }
      case STRING_RESULT:
      {
        enum enum_field_types type= group_item->field_type();
        if (type == MYSQL_TYPE_BLOB)
          key_length+= MAX_BLOB_WIDTH;		// Can't be used as a key
        else
        {
          /*
            Group strings are taken as varstrings and require an length field.
            A field is not yet created by create_tmp_field()
            and the sizes should match up.
          */
          key_length+= group_item->max_length + HA_KEY_BLOB_LENGTH;
        }
        break;
      }
      default:
        /* This case should never be choosen */
        DBUG_ASSERT(0);
        my_error(ER_OUT_OF_RESOURCES, MYF(ME_FATALERROR));
      }
    }
    parts++;
    if (group_item->maybe_null)
      null_parts++;
  }
  join->tmp_table_param.group_length=key_length+null_parts;
  join->tmp_table_param.group_parts=parts;
  join->tmp_table_param.group_null_parts=null_parts;
}