Function apply_selectivity_for_table

sql/sql_select.cc:8269–8317

*/

static double apply_selectivity_for_table(JOIN_TAB *s,
                                          uint use_cond_selectivity)
{
  double dbl_records;

  if (use_cond_selectivity > 1)
  {
    TABLE *table= s->table;
    double sel= table->cond_selectivity;
    double table_records= rows2double(s->records);
    DBUG_ASSERT(sel >= 0 && sel <= 1.0);
    /*
      table->cond_selectivity will include data from opt_range.
      Here we check that this is indeed the case.
      Note that if table_records == 0, then 'sel' is probably 1
    */
    DBUG_ASSERT(table_records == 0 ||
                sel <= s->table->opt_range_condition_rows /
                table_records);
    dbl_records= table_records * sel;
  }
  else
  {
    /*
      This is only taking into considering constant key parts used with
      this table!
      If no such conditions existed the following should normally hold:
      s->table->opt_range_condition_rows == s->found_rows ==
      s->records.
      The case when this does not hold is when using 'best splitting'
      in which case s->records may be less than s->found_rows;
    */
    DBUG_ASSERT(s->table->opt_range_condition_rows <= s->found_records);
    dbl_records= rows2double(MY_MIN(s->table->opt_range_condition_rows,
                                    s->records));
  }

  DBUG_ASSERT(dbl_records <= s->records);
  /*
    Ensure we return at least one row if there is any possibility to have
    a matching row.  Having rows >= 1.0 helps ensure that when we calculate
    total rows of joins, the number of resulting rows will not be less
    after the join. In other words, we assume there is at least one matching
    row when joining a row with the next table.
    0.0 is returned only if it is guaranteed there are no matching rows
    (for example if the table is empty).
  */
  return dbl_records ? MY_MAX(dbl_records, MIN_ROWS_AFTER_FILTERING) : 0.0;
}


/*