如何在 Postgresql 中做百分比

Question

我正在尝试创建一个查询。我有两张桌子

• customer (customer_id)
• rental (rental_date (时间戳), customer_id)

SELECT   to_char( rental_date, 'Month') AS month, 
         (count(Distinct customer.customer_id)/
           (count (distinct rental.customer_id) * 100) 
         ) AS percentage
FROM RENTAL,customer
GROUP BY month;

但结果为零。

Answer 1

当运算中涉及的所有“数字”都是整数时，结果也将是整数。

试试这个方法：

SELECT 
  to_char( rental_date, 'Month') AS month, 

  (
    count(distinct customer.customer_id)::float / 
   (count(distinct   rental.customer_id)::float * 100::float) 
  ) 
   as percentage 

FROM 
  RENTAL,customer 
GROUP BY month;