Method remove_duplicates

sql/sql_select.cc:28362–28462

*/

bool
JOIN_TAB::remove_duplicates()

{
  bool error;
  ulong keylength= 0, sort_field_keylength= 0;
  uint field_count, item_count;
  List<Item> *fields= (this-1)->fields;
  Item *item;
  THD *thd= join->thd;
  SORT_FIELD *sortorder, *sorder;
  DBUG_ENTER("remove_duplicates");

  DBUG_ASSERT(join->aggr_tables > 0 && table->s->tmp_table != NO_TMP_TABLE);
  THD_STAGE_INFO(join->thd, stage_removing_duplicates);

  if (!(sortorder= (SORT_FIELD*) my_malloc(PSI_INSTRUMENT_ME,
                                           (fields->elements+1) *
                                           sizeof(SORT_FIELD),
                                           MYF(MY_WME | MY_ZEROFILL))))
    DBUG_RETURN(TRUE);

  /* Calculate how many saved fields there is in list */
  field_count= item_count= 0;

  List_iterator<Item> it(*fields);
  for (sorder= sortorder ; (item=it++) ;)
  {
    if (!item->const_item())
    {
      if (item->get_tmp_table_field())
      {
        /* Field is stored in temporary table, skip */
        field_count++;
      }
      else
      {
        /* Item is not stored in temporary table, remember it */
        sorder->item= item;
        sorder->type= sorder->item->type_handler()->is_packable() ?
                      SORT_FIELD_ATTR::VARIABLE_SIZE :
                      SORT_FIELD_ATTR::FIXED_SIZE;
        /* Calculate sorder->length */
        item->type_handler()->sort_length(thd, item, sorder);
        sorder++;
        item_count++;
      }
    }
  }
  sorder->item= 0;                                 // End marker

  if ((field_count + item_count == 0) && ! having &&
      !(join->select_options & OPTION_FOUND_ROWS))
  {
    // only const items with no OPTION_FOUND_ROWS
    join->unit->lim.send_first_row();		// Only send first row
    my_free(sortorder);
    DBUG_RETURN(false);