Method std

sql/sql_analyse.cc:1059–1079

String *field_decimal::std(String *s, ha_rows rows)
{
  if (!(rows - nulls))
  {
    s->set_real((double) 0.0, 1,my_thd_charset);
    return s;
  }
  my_decimal num, tmp, sum2, sum2d;
  int prec_increment= current_thd->variables.div_precincrement;

  int2my_decimal(E_DEC_FATAL_ERROR, rows - nulls, FALSE, &num);
  my_decimal_mul(E_DEC_FATAL_ERROR, &sum2, sum+cur_sum, sum+cur_sum);
  my_decimal_div(E_DEC_FATAL_ERROR, &tmp, &sum2, &num, prec_increment);
  my_decimal_sub(E_DEC_FATAL_ERROR, &sum2, sum_sqr+cur_sum, &tmp);
  my_decimal_div(E_DEC_FATAL_ERROR, &tmp, &sum2, &num, prec_increment);
  double std_sqr= tmp.to_double();
  s->set_real(((double) std_sqr <= 0.0 ? 0.0 : sqrt(std_sqr)),
         MY_MIN(item->decimals + prec_increment, NOT_FIXED_DEC), my_thd_charset);

  return s;
}


int collect_string(void *element_, element_count, void *info_)