SQL-使用前面列中的值进行减法

我有一个查询，其中列出了国家名称、每个国家/地区的客户总数和活动客户数（它们存在于销售表中）

我需要一个列，其中应计算非活动客户的数量，但由于不能在同一select语句中使用已定义的别名，因此我陷入了困境

以下是查询：

SELECT  country_name , COUNT(DISTINCT cust.cust_id) AS TOTAL_NUM_CUSTOMERS ,                                                                                  
COUNT(DISTINCT sh.cust_id) AS NUM_ACTIVE_CUSTOMERS 

FROM countries ctr JOIN customers cust
ON (cust.country_id = ctr.country_id) 
LEFT JOIN  sales sh 
ON (sh.cust_id =  cust.cust_id)

GROUP BY  country name

---

我应该如何处理这个问题

根据您的方法，您可以：

SELECT ctr.country_name,
       COUNT(DISTINCT cust.cust_id) AS TOTAL_NUM_CUSTOMERS, 
       COUNT(DISTINCT sh.cust_id) AS NUM_ACTIVE_CUSTOMERS 
       (COUNT(DISTINCT cust.cust_id) - COUNT(DISTINCT sh.cust_id)) AS NUM_INACTIVE_CUSTOMERS 
FROM countries ctr JOIN
     customers cust
     ON cust.country_id = ctr.country_id LEFT JOIN
     sales sh 
     ON sh.cust_id =  cust.cust_id
GROUP BY ctr.country_name;

为了提高性能，我建议在加入

之前进行聚合：

SELECT ctr.country_name,
       COUNT(cust.cust_id) AS TOTAL_NUM_CUSTOMERS, 
       COUNT(sh.cust_id) AS NUM_ACTIVE_CUSTOMERS 
       (COUNT(cust.cust_id) - COUNT(sh.cust_id)) AS NUM_INACTIVE_CUSTOMERS 
FROM countries ctr JOIN
     customers cust
     ON cust.country_id = ctr.country_id LEFT JOIN
     (SELECT DISTINCT cust_id
      FROM sales sh 
     ) sh
     ON sh.cust_id =  cust.cust_id
GROUP BY country_name;

这样就不需要使用此情况下的
计数（独立）
子查询：

SELECT country_name,TOTAL_NUM_CUSTOMERS,NUM_ACTIVE_CUSTOMERS,
(TOTAL_NUM_CUSTOMERS-ACTIVE_CUSTOMERS) AS INACTIVE_CUSTOMERS FROM (
SELECT  country_name , COUNT(DISTINCT cust.cust_id) AS TOTAL_NUM_CUSTOMERS ,                                                                                  
COUNT(DISTINCT sh.cust_id) AS NUM_ACTIVE_CUSTOMERS 
FROM countries ctr JOIN customers cust
ON (cust.country_id = ctr.country_id) 
LEFT JOIN  sales sh 
ON (sh.cust_id =  cust.cust_id)
GROUP BY  country name ) AS A

将查询包装在外部查询中；这将允许您使用列别名：

SELECT  t.*,
        TOTAL_NUM_CUSTOMERS - NUM_ACTIVE_CUSTOMERS AS NUM_INACTIVE_CUSTOMERS
FROM    (
  SELECT  country_name,
          COUNT(DISTINCT cust.cust_id) AS TOTAL_NUM_CUSTOMERS,
          COUNT(DISTINCT sh.cust_id) AS NUM_ACTIVE_CUSTOMERS
  FROM    countries ctr
          JOIN customers cust
          ON (cust.country_id = ctr.country_id) 
          LEFT JOIN  sales sh 
          ON (sh.cust_id =  cust.cust_id)
  GROUP BY  country name
) t

您可以减去查询中的2个计数。编辑您的问题并提供示例数据和结果。计数（不同的cust.cust\u id）-计数（不同的sh.cust\u id）-像这样？我也这么认为，但SQLDeveloper说这是语法错误，出于某种原因不让我这么做谢谢，我实际上已经重新安装了SQLDeveloper，现在减法工作正常，但我没有考虑在加入之前进行聚合，再次感谢