查找相对百分比

Question

我进行了一项民意调查，投票结果来自用户。例如：

您想要菲亚特吗？

id | answer
1    yes
2    no 
3    yes
...
25   no

count = 20 yes / 5 no

(20 * 100) /25 = 80% Yes
(5 * 100) /25 = 20% No

因此，80％的人想要菲亚特，20％的人不想要。显然我可以做类似的事情：

select answer, count(*) as total from fast_survey group by answer;

但是这将显示计数，我正在寻找相对百分比。知道我该怎么做吗？

Answer 1

您可以COUNT在分区上获取每种答案类型的值：

SELECT DISTINCT answer,
       COUNT(*) OVER (partition BY answer) AS total,
       COUNT(*) OVER (partition BY answer) * 100 /
       COUNT(*) OVER () AS percentage
FROM fast_survey

Demo on SQLFiddle

如果要在百分比中获得更高的精度（对于上面的查询，它是整数除法，请将第一个COUNT强制转换为FLOAT：]]

SELECT DISTINCT answer,
       COUNT(*) OVER (partition BY answer) AS total,
       CAST(COUNT(*) OVER (partition BY answer) AS FLOAT) * 100 /
       COUNT(*) OVER () AS percentage
FROM fast_survey
Demo on SQLFiddle

Answer 2

SELECT round(count(*) FILTER (WHERE answer)     * 100.0 / count(*), 2) AS pct_yes
     , round(count(*) FILTER (WHERE NOT answer) * 100.0 / count(*), 2) AS pct_no
FROM   fast_survey;

Answer 3

怎么样：

Answer 4

只需将其与您在其中查找所有记录的表一起加入，而无需对答案进行除法并计算百分比...类似这样的事情