Function join_read_const

sql/sql_select.cc:25290–25335

*/

static int
join_read_const(JOIN_TAB *tab)
{
  int error;
  TABLE *table= tab->table;
  if (table->status & STATUS_GARBAGE)		// If first read
  {
    table->status= 0;
    if (cp_buffer_from_ref(tab->join->thd, table, &tab->ref))
      error=HA_ERR_KEY_NOT_FOUND;
    else
    {
      handler *file= table->file;
      if (table->covering_keys.is_set(tab->ref.key) && !table->no_keyread &&
          (int) table->reginfo.lock_type <= (int) TL_READ_HIGH_PRIORITY)
      {
        file->ha_start_keyread(tab->ref.key);
        /* This is probably needed for analyze table */
        tab->index= tab->ref.key;
      }
      error= file->
        ha_index_read_idx_map(table->record[0],tab->ref.key,
                              (uchar*) tab->ref.key_buff,
                              make_prev_keypart_map(tab->ref.key_parts),
                              HA_READ_KEY_EXACT);
      file->ha_end_keyread();
    }
    if (unlikely(error))
    {
      table->status= STATUS_NOT_FOUND;
      mark_as_null_row(tab->table);
      empty_record(table);
      if (error != HA_ERR_KEY_NOT_FOUND && error != HA_ERR_END_OF_FILE)
	return report_error(table, error);
      return -1;
    }
    store_record(table,record[1]);
  }
  else if (!(table->status & ~STATUS_NULL_ROW))	// Only happens with left join
  {
    table->status=0;
    restore_record(table,record[1]);			// restore old record
  }
  table->null_row=0;
  return table->status ? -1 : 0;
}

/*
  eq_ref access method implementation: "read_first" function