SQL - 如何計算x/y的標準差（stddev）？

Question

實例：計算點擊率（CTR）

CAST(SUM(num_clicks) as DOUBLE)/CAST(SUM(num_impression) as DOUBLE) as CTR 

我怎麼能計算點擊率的標準差？ stddev（CTR）將不起作用，因爲它將是嵌套的集成函數...此外，我無法先計算CTR，然後在其上運行stddev。

Answer 1

您可以先計算點擊率，然後使用子查詢運行STDDEV_POP。

SELECT STDDEV_POP(ctr) AS ctr_stddev 
FROM (
    SELECT CAST(SUM(num_clicks) as DOUBLE)/CAST(SUM(num_impression) as DOUBLE) AS ctr 
    FROM yourTable 
    WHERE ... 
    GROUP BY ad_id) AS temp