对 SUM 没有信心，不确定如何限制字段

Question

尝试为作业问题编写 SELECT 语句。我添加了一个 SUM 函数，但不确定它是否可以这样使用。由于表彼此相距较远，因此具有 3 个 JOIN。老实说，如果我当前的任何代码不正确，请告诉我。但我主要关注的是如何限制表格中“停产”的字段。

问题是：从销售数据模型中提取一份声明，显示客户名字、客户电子邮件地址、产品名称和总单位数，其中总单位数是库存单位和订购单位的总和。将记录限制为未停产的订单（即已停产字段中的“N”）。为 SELECT 子句中的每个字段创建一个别名，包括计算列的“总单位”。为 FROM 子句中的每个表创建并使用别名。按总单位排序。

表：https://imgur.com/rdZthcH

SELECT customerFN AS “First Name”, customerEmail AS “Email”, productName AS “Product Name”,
(SUM(unitsInStock)+SUM(unitsonorder)) AS "Total Units"
FROM customer c
JOIN order o
ON c.customerID = o.customerID
JOIN orderLine l
ON o.orderID = l.orderID
JOIN product p
ON l.productCode = p.productCode
WHERE 

WHERE 子句后面什么都没有，因为代码不完整。代码不完整，因为我认为我需要某种 WHERE 子句来限制“停止”字段。我只是不知道该怎么做。我查了 Where 子句，我认为它会使用 >

Answer 1

在我看来，您需要将 DISCONTINUED = 'N' 添加到您的 WHERE 子句中，或者换句话说

SELECT c.customerFN AS "First Name",
       c.customerEmail AS "Email",
       p.productName AS "Product Name",
       SUM(p.unitsInStock) + SUM(p.unitsonorder) AS "Total Units"
  FROM customer c
  JOIN order o
    ON c.customerID = o.customerID
  JOIN orderLine l
    ON o.orderID = l.orderID
  JOIN product p
    ON l.productCode = p.productCode
  WHERE p.DISCONTINUED = 'N'
  ORDER BY SUM(p.unitsInStock) + SUM(p.unitsonorder)

此外，您似乎正在使用某种文字处理器来创建代码，因为您的原始代码具有花哨的开引号和右引号字符（即“和”），而不是 ASCII 引号字符（即" )。我的大多数（任何？）编程语言或开发工具都不会接受那些文字处理器生成的字符。例如，看看你原来的问题——注意“名字”和“电子邮件”是如何没有突出显示为问题中的字符串，但“总单位”是？那是因为只有最后一个被双引号字符包围。我建议你坚持使用普通的 ASCII 编辑器，如 Windows 上的记事本，或任何数以千计的编程编辑器工具，你会更开心。

祝你好运。

Answer 2

调试此查询时，您很可能会遇到多个（不同的）错误消息。另外：在没有表/数据的情况下编写查询可能有点棘手，因为某些方面很容易被忽略。因此，我们将使用一些测试表（包括数据），请参阅dbfiddle here。 下面的查询代码将向您显示您可能会看到的各种错误 - 以及修复它们所需的 SQL。阅读代码中所有的cmets。

关系模型（缩短 id 列名）

ORA-00903：无效的表名

在您的原始查询中，您使用了一个名为 ORDER 的表。 ORDER 是保留字，请参阅documentation。命名表时避免使用它。

ORA-00937：不是单组函数

当使用有效的表名时，我们可以执行查询。在 WHERE 子句中添加一个条件（见下文）。由于 SELECT 和 ORDER BY 子句中的 SUM()，我们收到错误消息。显然，我们需要在查询中添加一个 GROUP BY 子句（这会立即导致下一条错误消息...）

SELECT 
  c.fn AS "First Name",
  c.email AS "Email",
  p.productName AS "Product Name",
  SUM(p.unitsInStock) + SUM(p.unitsonorder) AS "Total Units" --<- ORA-00937 
FROM customer c
  JOIN orders o     ON c.id = o.id -- table name fixed
  JOIN orderLine l  ON o.id = l.orderid
  JOIN product p    ON l.productCode = p.code
WHERE p.DISCONTINUED = 'N' --<- condition
ORDER BY SUM(p.unitsInStock) + SUM(p.unitsonorder) --<- ORA-00937
;

-- ORA-00937: not a single-group group function
--
-- Cause: A SELECT list cannot include both a group function, 
-- such as AVG, COUNT, MAX, MIN, SUM, STDDEV, or VARIANCE, 
-- and an individual column expression, 
-- unless the individual column expression is included in a GROUP BY clause.
-- see:
-- https://docs.oracle.com/cd/B10501_01/server.920/a96525/e900.htm

ORA-00979：不是 GROUP BY 表达式

SELECT 
  c.fn AS "First Name",
  c.email AS "Email",
  p.productName AS "Product Name",
  SUM(p.unitsInStock) + SUM(p.unitsonorder) AS "Total Units"
FROM customer c
  JOIN orders o     ON c.id = o.id
  JOIN orderLine l  ON o.id = l.orderid
  JOIN product p    ON l.productCode = p.code
WHERE p.DISCONTINUED = 'N'
group by p.productname  --<- causes ORA-00979
ORDER BY SUM(p.unitsInStock) + SUM(p.unitsonorder)
;
-- ORA-00979: not a GROUP BY expression
--
-- Make sure that columns ( listed in the SELECT clause ) that are _not_ "aggregated"
-- are listed in the GROUP BY clause, otherwise you may get an ORA-00937. 

查询有效 - 未选择任何行！

SELECT 
  c.fn AS "First Name",
  c.email AS "Email",
  p.productName AS "Product Name",
  SUM(p.unitsInStock) + SUM(p.unitsonorder) AS "Total Units"
FROM customer c
  JOIN orders o     ON c.id = o.id
  JOIN orderLine l  ON o.id = l.orderid
  JOIN product p    ON l.productCode = p.code
WHERE p.DISCONTINUED = 'N'
group by p.productname, c.fn, c.email
ORDER BY SUM(p.unitsInStock) + SUM(p.unitsonorder)
;

-- result
no rows selected

收尾工作

SELECT 
  c.fn AS "First Name",
  c.email AS "Email",
  p.productName AS "Product Name",
  SUM(p.unitsInStock) + SUM(p.unitsonorder) AS "Total Units"
FROM customer C
  JOIN orders O     ON C.id = O.customerid  --<- JOIN condition amended
  JOIN orderLine L  ON O.id = L.orderid
  JOIN product P    ON L.productCode = P.code
WHERE p.DISCONTINUED = 'N'
group by p.productname, c.fn, c.email
ORDER BY "Total Units" --<- you can use the column alias here - instead of SUM(...)
fetch first 10 rows only -- optional
;

-- result
First Name  Email                        Product Name  Total Units  
Annnora     agrime3@hc360.com            Beans         117          
Arleen      adahlback5@sciencedaily.com  Beans         117          
Gwendolin   gwalder0@unblog.fr           Beans         117          
Tomkin      tdeignan2@eepurl.com         Beans         117          
Alard       aaimeric9@cyberchimps.com    Beans         117          
Jeremiah    jolland4@dagondesign.com     Beans         117          
Melita      meason8@cnbc.com             Beans         117          
Stanwood    slanphere6@walmart.com       Beans         117          
Bobbi       bfireman1@bbb.org            Beans         117          
Idelle      ililly7@pen.io               Beans         117          


10 rows selected. 

请注意，您无需事先在表中插入任何行即可构建查询（请参阅dbfiddle）。您可能需要调整逻辑（等），以便查询完全满足要求。