Question

标准差分析可以是查找异常值的有用方法。有没有办法合并此查询的结果（找出远离平均值的第四个标准差的值）...

SELECT (AVG(weight_pounds) + STDDEV(weight_pounds) * 4) as high FROM [publicdata:samples.natality];

result = 12.721342001626912

...进入另一个查询，生成有关哪些州和哪个州出生的婴儿比平均值高出4个标准偏差的信息？

SELECT state, year, month ,COUNT(*) AS outlier_count
 FROM [publicdata:samples.natality]
WHERE
  (weight_pounds > 12.721342001626912)
AND
  (state != '' AND state IS NOT NULL)
GROUP BY state, year, month 
ORDER BY outlier_count DESC;

结果：

Row  state   year    month   outlier_count    
1    MD  1990    12  22   
2    NY  1989    10  17   
3    CA  1991    9   14

基本上将它组合成单个查询会很棒。

Answer 1

你可以滥用JOIN（因此性能会受到影响）：

SELECT n.state, n.year, n.month ,COUNT(*) AS outlier_count
FROM (
  SELECT state, year, month, weight_pounds, 1 as key 
  FROM [publicdata:samples.natality]) as n
JOIN (
  SELECT (AVG(weight_pounds) + STDDEV(weight_pounds) * 4) as giant_baby, 
          1 as key 
  FROM [publicdata:samples.natality]) as o
ON n.key = o.key
WHERE
  (n.weight_pounds > o.giant_baby)
AND
  (n.state != '' AND n.state IS NOT NULL)
GROUP BY n.state, n.year, n.month 
ORDER BY outlier_count DESC;

使用BigQuery查找具有标准差结果的异常值并结合WHERE子句

1 个答案: