Question

无法弄清楚为什么我的问题3遇到上述错误。

下面是我的代码

/* Question 1 */
CREATE TABLE CUSTOMERS 
( 
    CustomerID INT PRIMARY KEY, 
    CustFirstName VARCHAR(50) NOT NULL, 
    CustLastName VARCHAR(50) NOT NULL, 
    CustStreetAddress VARCHAR(50) NOT NULL, 
    CustCity VARCHAR(50) NOT NULL, 
    CustState VARCHAR(26) NOT NULL, 
    CustZipCode INT NOT NULL, 
    CustAreaCode INT NOT NULL, 
    CustPhoneNumber VARCHAR (26) NOT NULL
);  

CREATE TABLE EMPLOYEES 
( 
    EmployeeID INT PRIMARY KEY, 
    EmpFirstName VARCHAR(50) NOT NULL, 
    EmpLastName VARCHAR(50) NOT NULL, 
    EmpCity VARCHAR (50) NOT NULL, 
    EmpState VARCHAR(26) NOT NULL, 
    EmpZipCode INT NOT NULL, 
    EmpAreaCode INT NOT NULL, 
    EmpPhoneNumber VARCHAR(26) NOT NULL, 
    EmpBirthDate DATE NOT NULL
); 

CREATE TABLE ORDERS
( 
    OrderNumber INT PRIMARY KEY, 
    OrderDate DATE NOT NULL, 
    ShipDate DATE NOT NULL, 
    CustomerID INT NOT NULL, 
    EmployeeID INT NOT NULL, 

    FOREIGN KEY(EmployeeID) REFERENCES EMPLOYEES(EmployeeID), 
    FOREIGN KEY(CustomerID) REFERENCES CUSTOMERS(CustomerID)
); 

CREATE TABLE CATEGORIES
( 
    CategoryID INT PRIMARY KEY, 
    CategoryDescription VARCHAR(255) NOT NULL
); 

CREATE TABLE PRODUCTS
(
    ProductNumber INT PRIMARY KEY, 
    ProductName VARCHAR(50) NOT NULL, 
    ProductDescription VARCHAR(255) NOT NULL,
    RetailPrice INT NOT NULL, 
    QuantityOnHand INT NOT NULL, 
    CategoryID INT NOT NULL, 

    FOREIGN KEY(CategoryID) REFERENCES CATEGORIES (CategoryID)
);    

CREATE TABLE ORDER_DETAILS
( 
    OrderNumber INT NOT NULL, 
    ProductNumber INT NOT NULL, 
    QuotedPrice INT NOT NULL, 
    QuantityOrdered INT NOT NULL, 

    PRIMARY KEY (OrderNumber, ProductNumber), 
    FOREIGN KEY (OrderNumber) REFERENCES ORDERS(OrderNumber), 
    FOREIGN KEY(ProductNumber) REFERENCES PRODUCTS(ProductNumber)
);   

CREATE TABLE VENDORS
(
    VendorID INT PRIMARY KEY, 
    VendName VARCHAR(100) NOT NULL, 
    VendStreetAddress VARCHAR(50) NOT NULL, 
    VendCity VARCHAR(50) NOT NULL, 
    VendState VARCHAR(26) NOT NULL, 
    VendFaxNumber VARCHAR(50) NOT NULL, 
    VendWebPage VARCHAR(100) NOT NULL, 
    VendEmailAddress VARCHAR(100) NOT NULL
); 

CREATE TABLE PRODUCT_VENDORS
(
    ProductNumber INT NOT NULL, 
    VendorID INT NOT NULL, 
    WholeSalePrice INT NOT NULL,
    DaysToDeliver INT NOT NULL, 

    PRIMARY KEY(ProductNumber, VendorID), 
    FOREIGN KEY(ProductNumber) REFERENCES PRODUCTS(ProductNumber), 
    FOREIGN KEY(VendorID) REFERENCES Vendors(VendorID)
); 

/* QUESTION 2 */

SELECT 
    OrderDate, CustFirstName, CustLastName
FROM 
    CUSTOMERS C, ORDERS O
WHERE 
    C.CustomerID = O.OrderNumber; 

/* QUESTION 3 */

SELECT 
    ProductNumber, WholeSalePrice, VendName 
FROM 
    PRODUCTS P, PRODUCT_VENDORS PV, VENDORS V 
WHERE 
    P.PRODUCTNUMBER = PV.ProductNumber AND PV.VendorID = V.VendorID;

我得到了错误

列名“ ProductNumber”不明确

Answer 1

因为在您的查询中有两个表的列名称为ProductNumber，所以您需要告诉数据库引擎您想要获取哪一列。

此外，使用JOIN而不是,逗号CROSS JOIN，因为Join比两个表之间的关系逗号更清楚

SELECT PV.ProductNumber, WholeSalePrice, VendName 
FROM PRODUCTS P 
JOIN PRODUCT_VENDORS PV ON P.PRODUCTNUMBER = PV.ProductNumber
JOIN VENDORS V ON PV.VendorID = V.VendorID;

Answer 2

您的查询规定SELECT ProductNumber在两个都有ProductNumber的表中。在“ SELECT列”列表中，在ProductNumber前面加上要从其接收数据的表名。

也请看一下您的问题2。我不认为您真的想将客户ID联接到订单号，您应该在JOIN子句中使用WHERE语法表示联接

Answer 3

模棱两可的错误意味着您正在调用表中都存在的某个字段，而SQL不知道从何处获取它。看到，通过查询，您只是在字面上调用ProductNumber字段，因为两个表上都有ProductNumber字段，因此SQL不知道在哪里获取它，并且您未指定任何字段桌子。

因此，当您在多个表中具有相同的列时，最好使用表序号1st，然后再使用诸如table1.col1，table2.col2之类的列所以就您而言

 SELECT p.ProductNumber, WholeSalePrice, v.VendName     
   FROM PRODUCTS P join 
  PRODUCT_VENDORS PV  on P.PRODUCTNUMBER = PV.ProductNumber //
  join   VENDORS V on PV.VendorID = V.VendorID //use join instead your's

列名不明确'ProductNumber'

3 个答案: