Ignite：SQL查询来计算列的概率

Question

Gender
-------
Female
Male
Male
Male
Female
Female
Male
Female

在这里我想计算性别列的机率，并尝试以下查询，但是它不起作用。

SELECT (count(*)/(SELECT count(*) from DIABETIC_TOPIC) as probability from DIABETIC_TOPIC group by gender order by gender;

我错过了什么？

Answer 1

我会在非分组查询中交叉加入分组查询，并将其划分：

SELECT     gender, cnt_gender / cnt * 100 AS probability
FROM       (SELECT   gender, COUNT(*)
            FROM     diabetic_topic
            GROUP BY gender) a
CROSS JOIN (SELECT COUNT(*) AS cnt
            FROM   diabetic_topic) b