SQL - 如何计算x / y的标准差（stddev）？

Question

示例：计算点击率（CTR）

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

如何计算CTR的标准偏差？ stddev（CTR）不会工作，因为它将是一个嵌套的混合函数...而且，我不能先计算CTR然后再运行stddev。

Answer 1

您可以先计算点击率，然后使用子查询在其上运​​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