在 PostgreSQL 中按月透视用户收入

问题描述

在 Postgresql 中编写查询时，我使用以下语法。这个查询工作得很好。我唯一的问题是下面出现的空值。

我想在这个查询中使用 Coalesce() 但我被卡住了。有没有办法调整这个查询，以便我可以将 Coalesce 添加到这个查询中？

-- Import tablefunc
CREATE EXTENSION IF NOT EXISTS tablefunc;

SELECT * FROM CROsstAB($$
  SELECT
    user_id,DATE_Trunc('month',order_date) :: DATE AS delivr_month,SUM(meal_price * order_quantity) :: FLOAT AS revenue
  FROM meals
  JOIN orders ON meals.meal_id = orders.meal_id
 WHERE user_id IN (0,1,2,3,4)
   AND order_date < '2018-09-01'
 GROUP BY user_id,delivr_month
 ORDER BY user_id,delivr_month;
$$)
-- Select user ID and the months from June to August 2018
AS ct (user_id INT,"2018-06-01" FLOAT,"2018-07-01" FLOAT,"2018-08-01" FLOAT)     
ORDER BY user_id ASC;

输出：

解决方法

SELECT 
       user_id,coalesce("2018-06-01",0.0) "2018-06-01",coalesce("2018-07-01",0.0) "2018-07-01",coalesce("2018-08-01",0.0) "2018-08-01"
 FROM CROSSTAB($$
  SELECT
    user_id,DATE_TRUNC('month',order_date) :: DATE AS delivr_month,SUM(meal_price * order_quantity) :: FLOAT AS revenue
  FROM meals
  JOIN orders ON meals.meal_id = orders.meal_id
 WHERE user_id IN (0,1,2,3,4)
   AND order_date < '2018-09-01'
 GROUP BY user_id,delivr_month
 ORDER BY user_id,delivr_month;
$$)
-- Select user ID and the months from June to August 2018
AS ct (user_id INT,"2018-06-01" FLOAT,"2018-07-01" FLOAT,"2018-08-01" FLOAT)     
ORDER BY user_id ASC;