Function check_quick_select

sql/opt_range.cc:12430–12571

*/

static
ha_rows check_quick_select(PARAM *param, uint idx, ha_rows limit,
                           bool index_only,
                           SEL_ARG *tree, bool update_tbl_stats, 
                           uint *mrr_flags, uint *bufsize, Cost_estimate *cost,
                           bool *is_ror_scan)
{
  SEL_ARG_RANGE_SEQ seq;
  RANGE_SEQ_IF seq_if=
    {NULL, sel_arg_range_seq_init, sel_arg_range_seq_next, 0, 0};
  handler *file= param->table->file;
  ha_rows rows= HA_POS_ERROR;
  uint keynr= param->real_keynr[idx];
  DBUG_ENTER("check_quick_select");

  /* Range not calculated yet */
  param->quick_rows[keynr]= HA_POS_ERROR;

  /* Handle cases when we don't have a valid non-empty list of range */
  if (!tree)
    DBUG_RETURN(HA_POS_ERROR);
  if (tree->type == SEL_ARG::IMPOSSIBLE)
    DBUG_RETURN(0L);
  if (tree->type != SEL_ARG::KEY_RANGE || tree->part != 0)
    DBUG_RETURN(HA_POS_ERROR);

  seq.keyno= idx;
  seq.real_keyno= keynr;
  seq.key_parts= param->key[idx];
  seq.param= param;
  seq.start= tree;

  param->range_count=0;
  param->max_key_parts=0;

  seq.is_ror_scan= TRUE;
  if (param->table->key_info[keynr].index_flags & HA_KEY_SCAN_NOT_ROR)
    seq.is_ror_scan= FALSE;
  
  *mrr_flags= param->force_default_mrr? HA_MRR_USE_DEFAULT_IMPL: 0;
  /*
    Pass HA_MRR_SORTED to see if MRR implementation can handle sorting.
  */
  *mrr_flags|= HA_MRR_NO_ASSOCIATION | HA_MRR_SORTED;

  // TODO: param->max_key_parts holds 0 now, and not the #keyparts used.
  // Passing wrong second argument to index_flags() makes no difference for
  // most storage engines but might be an issue for MyRocks with certain
  // datatypes.
  // Note that HA_KEYREAD_ONLY implies that this is not a clustered index
  if (index_only && 
      (file->index_flags(keynr, param->max_key_parts, 1) & HA_KEYREAD_ONLY))
     *mrr_flags |= HA_MRR_INDEX_ONLY;
  
  if (param->thd->lex->sql_command != SQLCOM_SELECT)
    *mrr_flags |= HA_MRR_USE_DEFAULT_IMPL;

  *bufsize= param->thd->variables.mrr_buff_size;