Question

我的代码写成：

SELECT name, age,
  CASE WHEN abs(10 - mean(valueLeft)) < abs(10 - mean(valueRight)) THEN stddev(valueLeftMagnitude) ELSE stddev(valueRightMagnitude) END as value1,
  CASE WHEN abs(10 - mean(valueLeft)) < abs(10 - mean(valueRight)) THEN mean(valueLeftMagnitude) ELSE mean(valueRightMagnitude) END as value2,
  CASE WHEN abs(10 - mean(valueLeft)) < abs(10 - mean(valueRight)) THEN median(valueLeftMagnitude) ELSE median(valueRightMagnitude) END as value3
FROM table
GROUP BY name, age

由于所有三个CASE中的WHEN语句相同，我不想重复它们。有没有办法做到这一点？

示例：我想要像 -

这样的东西

SELECT name, age,
  CASE WHEN abs(10 - mean(valueLeft)) < abs(10 - mean(valueRight))
    THEN stddev(valueLeftMagnitude) ELSE stddev(valueRightMagnitude) END as value1,
    THEN mean(valueLeftMagnitude) ELSE mean(valueRightMagnitude) END as value2,
    THEN median(valueLeftMagnitude) ELSE median(valueRightMagnitude) END as value3
FROM table
GROUP BY name, age

请帮忙。

Answer 1

嵌入式选择可以确保您只进行一次case计算：

SELECT perprocessed.name, perprocessed.age, stddev(perprocessed.valueMagnitude), mean(perprocessed.valueMagnitude), median(perprocessed.valueLeftMagnitude) from
(SELECT
  name,
  age,
  CASE WHEN abs(10 - mean(valueLeft)) < abs(10 - mean(valueRight)) THEN valueLeftMagnitude ELSE valueRightMagnitude END as valueMagnitude
  FROM table) as perprocessed
GROUP BY perprocessed.name, perprocessed.age

Answer 2

您的查询非常易读，我认为复制粘贴表达式并没有什么不妥。如果您只想进行一次此评估，则查询会稍微复杂一些，因为您需要分两步执行：

SELECT
  CASE WHEN which = 'left' THEN stddev_left ELSE stddev_right END AS value1,
  CASE WHEN which = 'left' THEN mean_left   ELSE mean_right   END AS value2,
  CASE WHEN which = 'left' THEN median_left ELSE median_right END AS value3
FROM
(
  SELECT 
    name, 
    age, 
    CASE WHEN abs(10 - mean(valueLeft)) < abs(10 - mean(valueRight)) 
         THEN 'left' ELSE 'right' END AS which,
    stddev(valueLeftMagnitude) AS stddev_left,
    stddev(valueRightMagnitude) AS stddev_right,
    mean(valueLeftMagnitude) AS mean_left,
    mean(valueRightMagnitude) AS mean_right,
    median(valueLeftMagnitude) AS median_left,
    median(valueRightMagnitude) median_right
  FROM table 
  GROUP BY name, age
) grouped;

如何在多个THEN中查询CASE WHEN？

2 个答案: