SELECT
  category,cnt_A,cnt_B,ROUND(avg_A) AS avg_a, ROUND(avg_B) AS avg_b,ROUND(std_A) AS std_a, ROUND(std_B) AS std_b,
  IF(cnt_A+cnt_B<100,'t','z') AS dist,
  IF(cnt_A+cnt_B<100,
   --t statistics--
   0,
    --z statistics--
    ROUND( ABS(avg_A-avg_B)/SQRT( std_A*std_A/(1.0*cnt_A) + std_B*std_B/(1.0*cnt_B) ) ,2)
  ) AS stat_t
FROM itmd_para_avg_diff_test
WHERE 100<=cnt_A+cnt_B
ORDER BY stat_t DESC