SQL：選擇語句返回 2 列值的比率

Question

我有一個電子測試數據表，其中包含給定電壓下成對組件的通過/失敗結果。 它看起來像這樣：

Component_A|Component_B|Voltage|Result
1           2           1.0     Pass
1           2           1.0     Pass
1           2           1.0     Fail
1           2           1.0     Fail
1           2           2.0     Pass
1           2           2.0     Pass
1           2           2.0     Pass
1           2           2.0     Pass
3           4           1.0     Pass
3           4           1.0     Pass
3           4           1.0     Pass
3           4           1.0     Pass
3           4           2.0     Pass
3           4           2.0     Pass
3           4           2.0     Pass
3           4           2.0     Pass

對於每個Component_A ， Component_B ， Voltage ，我想顯示對於給定的故障率Component_A/Component_B/Voltage組合以及用於該組合的失敗比率Component_A/Component_B 。 預期輸出如下：

Component_A|Component_B|Voltage|Voltage_Fail_Ratio|Component_Fail_Ratio
1           2           1.0     2/4(0.5)            2/8(0.25)
1           2           2.0     0/4(0)              0/8(0)
3           4           1.0     4/4(0)              0/8(0)
3           4           2.0     0/4(0)              0/8(0)

有一些選項會很棒（使用聯合或子查詢……選項越多越好）。 我已經嘗試編寫一個子查詢來至少獲得電壓故障率，但它沒有報告沒有故障的組件/電壓組合，我不確定如何獲得組件故障率：

SELECT f.component_a,f.component_b,f.voltage,f.failcount,p.passcount, f.failcount/(f.failcount+p.passcount) FROM 
 ((SELECT component_a,component_b,voltage, count(*) as failcount from `tests` where 
  result='FAIL' 
 GROUP BY component_a,component_b,voltage) f INNER JOIN  
 (SELECT component_a,component_b,voltage, count(*) as passcount from `tests` where 
  result='PASS' 
 GROUP BY component_a,component_b,voltage) p on p.component_a=f.component_a and p.component_b=f.component_b and 
 p.voltage=f.voltage);

http://sqlfiddle.com/#!9/623ae/1

Answer 1

我認為這就是您想要的 - 它在兩個單獨的子查詢中計算Voltage_Fail_Ratio和Component_Fail_Ratio ，然后在匹配的component_a和component_b值上連接：

SELECT t1.component_a, t1.component_b, t1.Voltage, t1.Voltage_Fail_Ratio, Component_Fail_Ratio
FROM (
  SELECT component_a, component_b, Voltage,
         SUM(result = 'FAIL') / COUNT(*) AS Voltage_Fail_Ratio
  FROM tests
  GROUP BY component_a, component_b, Voltage
  ) t1
JOIN (
  SELECT component_a, component_b,
         SUM(result = 'FAIL') / COUNT(*) AS Component_Fail_Ratio
  FROM tests
  GROUP BY component_a, component_b
  ) t2 ON t2.component_a = t1.component_a AND t2.component_b = t1.component_b
;

輸出：

component_a     component_b     Voltage     Voltage_Fail_Ratio  Component_Fail_Ratio
1               2               1           0.5                 0.25
1               2               2           0                   0.25
3               4               1           0                   0
3               4               2           0                   0

SQLFiddle 上的演示

Answer 2

這在某種程度上與@Nick 的類似，但使用 WITH 的視圖。 只是為了給你更多的選擇。

WITH for_volt_fail_ratio AS(
  SELECT com_a, com_b, volt, SUM(result = 'FAIL') / COUNT(*) AS Voltage_Fail_Ratio
  FROM tests
  GROUP BY com_a, com_b, volt),
 for_com_fail_ratio AS(
  SELECT com_a, com_b,SUM(result = 'FAIL') / COUNT(*) AS Component_Fail_Ratio
  FROM tests
  GROUP BY com_a, com_b),
 sh AS(
   SELECT tb1.com_a,tb1.com_b,tb1.volt,tb1.Voltage_Fail_Ratio,tb2.Component_Fail_Ratio
   FROM for_volt_fail_ratio tb1 INNER JOIN for_com_fail_ratio tb2 ON (tb1.com_a=tb2.com_a AND tb1.com_b=tb2.com_b)
  )
 SELECT * FROM sh

演示

Answer 3

最簡單的方法是條件聚合：

select component_a, component_b, voltage,
        sum(case when result = 'PASS' then 1 else 0 end) as num_pass,
        sum(case when result = 'FAIL' then 1 else 0 end) as num_fail,
        avg(case when result = 'FAIL' then 1.0 else 0 end) as fail_rate
from tests
group by component_a, component_b, voltage;

如果您確實在使用 MySQL（正如 SQL Fiddle 建議的那樣），您可以將其簡化為：

select component_a, component_b, voltage,
        sum(result = 'PASS') as num_pass,
        sum(result = 'FAIL') as num_fail,
        avg(result = 'FAIL') as fail_rate
from tests
group by component_a, component_b, voltage