如何在SQL中过滤经过数学计算的数据？

这可能比我想象的要容易，但我被难倒了。我编写了以下查询，该查询汇总了某个客户在某个特定商店所做的所有购买，以及同一客户在同一商店所做的退货总额，最后，将从总购买量中减去总退货的结果存储在一个名为total_Exponed的计算列中。我的问题是：

SELECT Account_Id,
  SUM(CASE WHEN Transaction_Code = 'Purchase' THEN Transaction_Amount ELSE 0 END) AS TOTAL_PURCHASED,
  SUM(CASE WHEN Transaction_Code = 'Return' THEN Transaction_Amount ELSE 0 END) AS TOTAL_RETURNED,
  (TOTAL_PURCHASED - TOTAL_RETURNED) AS TOTAL_SPENT
FROM Transactions_Table
WHERE Store = 'Store XYZ'
GROUP BY Account_Id
ORDER BY TOTAL_SPENT DESC

---

我的问题是，这个查询返回数十万条记录，但我只关心大约10%的返回数据。所以，假设您只希望看到返回的数据，其中TOTAL_Consumed>=500.00。但就我个人而言，我不知道该怎么做！在SQL中，

WHERE

子句在

SELECT

子句之前处理。因此，当SQL开始从表中筛选与查询相关的行时，它还不知道列

TOTAL\u-spend

有几种方法可以解决这个问题

1）重复

WHERE

子句中的表达式，而不是引用

SELECT

子句中的列名：

SELECT Account_Id,
  SUM(CASE WHEN Transaction_Code = 'Purchase' THEN Transaction_Amount ELSE 0 END) AS TOTAL_PURCHASED,
  SUM(CASE WHEN Transaction_Code = 'Return' THEN Transaction_Amount ELSE 0 END) AS TOTAL_RETURNED,
  (TOTAL_PURCHASED - TOTAL_RETURNED) AS TOTAL_SPENT
FROM Transactions_Table
WHERE Store = 'Store XYZ'
GROUP BY Account_Id
ORDER BY 
  (SUM(CASE WHEN Transaction_Code = 'Purchase' THEN Transaction_Amount ELSE 0 END) - SUM(CASE WHEN Transaction_Code = 'Return' THEN Transaction_Amount ELSE 0 END)) DESC

注意：如果您要查找花费总额超过500的组，请使用

HAVING

子句而不是

WHERE

2）使用视图。删除

WHERE

子句，并使用查询创建一个

视图。然后，从该视图中选择并添加
WHERE
子句

CREATE VIEW Whatever AS
   SELECT Account_Id,
      SUM(CASE WHEN Transaction_Code = 'Purchase' THEN Transaction_Amount ELSE 0 END) AS    TOTAL_PURCHASED,
      SUM(CASE WHEN Transaction_Code = 'Return' THEN Transaction_Amount ELSE 0 END) AS TOTAL_RETURNED,
      (TOTAL_PURCHASED - TOTAL_RETURNED) AS TOTAL_SPENT
   FROM Transactions_Table
   GROUP BY Account_Id;

SELECT * From Whatever WHERE TOTAL_SPENT >= 500

3）使用嵌套选择：

select * from (
  SELECT
    Account_Id,
    SUM(CASE WHEN Transaction_Code = 'Purchase' THEN Transaction_Amount ELSE 0 END) AS TOTAL_PURCHASED,
    SUM(CASE WHEN Transaction_Code = 'Return' THEN Transaction_Amount ELSE 0 END) AS TOTAL_RETURNED,
    (TOTAL_PURCHASED - TOTAL_RETURNED) AS TOTAL_SPENT
  FROM Transactions_Table
  WHERE Store = 'Store XYZ'
  GROUP BY Account_Id
) where TOTAL_SPENT > 500 ORDER BY TOTAL_SPENT DESC;

4）如果您的数据库支持，请使用CTE：

WITH MyQuery AS (
  SELECT
    Account_Id,
    SUM(CASE WHEN Transaction_Code = 'Purchase' THEN Transaction_Amount ELSE 0 END) AS TOTAL_PURCHASED,
    SUM(CASE WHEN Transaction_Code = 'Return' THEN Transaction_Amount ELSE 0 END) AS TOTAL_RETURNED,
    (TOTAL_PURCHASED - TOTAL_RETURNED) AS TOTAL_SPENT
  FROM Transactions_Table
  WHERE Store = 'Store XYZ'
  GROUP BY Account_Id
)
SELECT * FROM MyQuery WHERE TOTAL_SPENT > 500 ORDER BY TOTAL_SPENT DESC;

谢谢你，先生！正如您所建议的，我尝试创建一个视图，但不幸的是，我没有获得足够高的访问级别来创建视图。我尝试了嵌套的select next，它给出了我想要的确切结果。