Function join_init_read_record

sql/sql_select.cc:25719–25806

int join_init_read_record(JOIN_TAB *tab)
{
  bool need_unpacking= FALSE;
  JOIN *join= tab->join;
  /* 
    Note: the query plan tree for the below operations is constructed in
    save_agg_explain_data.
  */
  if (tab->distinct && tab->remove_duplicates())  // Remove duplicates.
    return 1;

  if (join->top_join_tab_count != join->const_tables)
  {
    TABLE_LIST *tbl= tab->table->pos_in_table_list;
    need_unpacking= tbl ? tbl->is_sjm_scan_table() : FALSE;
  }

  if (tab->need_to_build_rowid_filter)
  {
    if (tab->build_range_rowid_filter())
      return 1;  /* Fatal error */
  }

  if (tab->filesort && tab->sort_table())     // Sort table.
    return 1;

  DBUG_EXECUTE_IF("kill_join_init_read_record",
                  tab->join->thd->set_killed(KILL_QUERY););


  if (!tab->preread_init_done  && tab->preread_init())
    return 1;

  if (tab->select && tab->select->quick && tab->select->quick->reset())
  {
    /* Ensures error status is propagated back to client */
    report_error(tab->table,
                 tab->join->thd->killed ? HA_ERR_QUERY_INTERRUPTED : HA_ERR_OUT_OF_MEM);
    return 1;
  }
  /* make sure we won't get ER_QUERY_INTERRUPTED from any code below */
  DBUG_EXECUTE_IF("kill_join_init_read_record",
                  tab->join->thd->reset_killed(););

  Copy_field *save_copy, *save_copy_end;
  
  /*
    init_read_record resets all elements of tab->read_record().
    Remember things that we don't want to have reset.
  */
  save_copy=     tab->read_record.copy_field;
  save_copy_end= tab->read_record.copy_field_end;
  
  /*
    JT_NEXT means that we should use an index scan on index 'tab->index'
    However if filesort is set, the table was already sorted above
    and now have to retrieve the rows from the tmp file or by rnd_pos()
    If !(tab->select && tab->select->quick)) it means that we are