根据一列中的值按组计算百分比

Question

对基本问题的道歉，搜索后我找不到答案。

具有2列car_type和event的简单表。每次客户询问汽车时，都会在表中放入一条记录，并且event =“ inquire”。如果购买了该类型的汽车，则会放入事件=“购买”的记录。

根据＃购买/＃查询，我将如何计算哪种车型最成功？按课程类型分组。

我已经尝试过

select car_type, 
      ((select count(*) from TABLE where event = "bought" ) / 
       (select count(*) from alerts where event = "inquire") * 100.0) as percentage
from TABLE 
group by car_type;

但是这没有用。

谢谢你！

Answer 1

您可以使用条件聚合：

select car,
       (sum( event = 'bought') /
        sum( event = 'inquire' )
       ) as bought_inquire_ratio
from t
group by car;

如果您只是想整体购买比率，可以使用：

select car,
       avg( event = 'bought' )
from t
group by car;

Answer 2

您可以将每辆车的不同事件类型相加（最容易在子查询中），然后将结果除以得到百分比，按该值的降序排列并仅取最高值：

SELECT car_type, 100.0 * bought / inquiries AS percentage
FROM (
    SELECT car_type,
           SUM(event = 'bought') AS bought,
           SUM(event = 'inquire') AS inquiries
    FROM alerts
    GROUP BY car_type
) c
ORDER BY percentage DESC
LIMIT 1