Function compute_window_func

sql/sql_window.cc:2877–2977

TODO(cvicentiu) update this comment to reflect the new execution. Streamed window function computation with window frames. We make a single pass over the ordered temp.table, but we're using three cursors: - current row - the row that we're computing window func value for) - start_bound - the start of the frame - bottom_bound - the end of the frame All three cursors move toget

*/
bool compute_window_func(THD *thd,
                         List<Item_window_func>& window_functions,
                         List<Cursor_manager>& cursor_managers,
                         TABLE *tbl,
                         SORT_INFO *filesort_result)
{
  List_iterator_fast<Item_window_func> iter_win_funcs(window_functions);
  List_iterator_fast<Cursor_manager> iter_cursor_managers(cursor_managers);
  bool ret= false;
  uint err;

  READ_RECORD info;

  if (init_read_record(&info, current_thd, tbl, NULL/*select*/, filesort_result,
                       0, 1, FALSE))
    return true;

  Cursor_manager *cursor_manager;
  while ((cursor_manager= iter_cursor_managers++))
    cursor_manager->initialize_cursors(&info);

  /* One partition tracker for each window function. */
  List<Group_bound_tracker> partition_trackers;
  Item_window_func *win_func;
  while ((win_func= iter_win_funcs++))
  {
    Group_bound_tracker *tracker= new Group_bound_tracker(thd,
                                        win_func->window_spec->partition_list);
    // TODO(cvicentiu) This should be removed and placed in constructor.
    tracker->init();
    partition_trackers.push_back(tracker);
  }

  List_iterator_fast<Group_bound_tracker> iter_part_trackers(partition_trackers);
  ha_rows rownum= 0;
  uchar *rowid_buf= (uchar*) my_malloc(PSI_INSTRUMENT_ME, tbl->file->ref_length, MYF(0));

  while (true)
  {
    if ((err= info.read_record()))
      break; // End of file.

    /* Remember current row so that we can restore it before computing
       each window function. */
    tbl->file->position(tbl->record[0]);
    memcpy(rowid_buf, tbl->file->ref, tbl->file->ref_length);

    iter_win_funcs.rewind();
    iter_part_trackers.rewind();
    iter_cursor_managers.rewind();

    Group_bound_tracker *tracker;
    while ((win_func= iter_win_funcs++) &&
           (tracker= iter_part_trackers++) &&
           (cursor_manager= iter_cursor_managers++))
    {
      if (tracker->check_if_next_group() || (rownum == 0))
      {