用sql计算市场渗透率？

Question

我有购买活动的表'transactions'：

customer_id, company, purchaseamount

我正在寻找一个sql命令来输出＆＃34;市场渗透率＆＃34;对于某个公司：

例如，我想计算：

（从公司购买的唯一customer_id的数量== 12）/（唯一customer_id的总数）

Answer 1

select count(distinct customer_id) * 100  / (select count(distinct customer_id) from transactions)
from transactions
where customer_id = 12

Answer 2

您可以使用条件聚合执行此操作：

select count(distinct case when company = 12 then customer_id end) / count(distinct customer_id)
from transactions;

Answer 3

customer_id的唯一编号是一行，因此您可以cross join使用每个公司的不同计数

SELECT     company, COUNT (DISTINCT customer_id) / cnt AS penetration_ratio
FROM       my_table
CROSS JOIN (SELECT COUNT (DISTINCT customer_id) AS cnt 
            FROM   my_table) t