Question

这可能比我想象的要容易，但我很难过。我写了以下查询，该查询总结了客户在特定商店所做的所有购买，以及同一客户在同一商店的总回报，最后，存储了从总数中减去总回报的结果在名为TOTAL_SPENT的计算列中购买。这是我的疑问：

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了数十万条记录，但我只关心大约10％的数据返回。所以，假设您只想看到TOTAL_SPENT＆gt; = 500.00返回的数据。但对于我的生活，我无法弄清楚如何做到这一点！ 垂头丧气

Answer 1

在SQL中，WHERE子句在 SELECT子句之前处理。因此，当SQL开始过滤您的表中与您的查询相关的行时，它尚未知道列TOTAL_SPENT。

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<{1>}超过500的群组，请使用TOTAL_SPENT子句代替{{1 }}

2）使用视图。删除HAVING子句并使用您的查询创建WHERE。然后，从视图中选择并添加WHERE子句。

VIEW

3）使用嵌套的SELECT：

WHERE

4）如果您的数据库支持它，请使用CTE：
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

如何在SQL中过滤数学计算的数据？

1 个答案: