mysql关系有问题吗？

我需要两个表，一个用三个表显示一对多关系，另一个表显示多对多关系。我已经成功地完成了前两个任务，一个查询只涉及一个表，一个一对多查询涉及两个表

一个表查询：

SELECT LastName, FirstName, City 
FROM Customer
WHERE City = 'Lutherville-Timonium'

一对多涉及2个表：

SELECT b.BrandName, m.ModelName
FROM Brand b, Model m
WHERE b.BrandID = m.BrandID

这是我的密码：

    DROP DATABASE IF EXISTS FinalProject;

CREATE DATABASE IF NOT EXISTS FinalProject;

Use FinalProject;

CREATE TABLE IF NOT EXISTS Brand
(
 BrandID INT,
 BrandName VARCHAR(45),
 PRIMARY KEY(BrandID)
);

CREATE TABLE IF NOT EXISTS Model
(
 ModelName VARCHAR(45),
 BrandID INT,
 PRIMARY KEY(ModelName),
 FOREIGN KEY(BrandID) REFERENCES Brand(BrandID)
);

CREATE TABLE IF NOT EXISTS Platform
(
 PlatformID INT,
 Platform VARCHAR(45),
 PRIMARY KEY(PlatformID)
);

CREATE TABLE IF NOT EXISTS Computer
(
 ComputerID INT,
 ModelName VARCHAR(45),
 PlatformID INT,
 Processor VARCHAR(45),
 Memory VARCHAR(45),
 HardDrive VARCHAR(45),
 OperatingSystem VARCHAR(45),
 PRIMARY KEY(ComputerID),
 FOREIGN KEY(ModelName) REFERENCES Model(ModelName),
 FOREIGN KEY(PlatformID) REFERENCES Platform(PlatformID)
);

CREATE TABLE IF NOT EXISTS Customer
(
 CustomerID INT,
 LastName VARCHAR(45),
 FirstName VARCHAR(45),
 Address VARCHAR(45),
 Zip INT,
 City VARCHAR(45),
 State VARCHAR(2),
 PhoneNumber INT,
 Email VARCHAR(45),
 PRIMARY KEY(CustomerID)
);

CREATE TABLE IF NOT EXISTS Employee
(
 EmployeeID INT,
 Position VARCHAR(45),
 LastName VARCHAR(45),
 FirstName VARCHAR(45),
 Address VARCHAR(45),
 Zip INT,
 City VARCHAR(45),
 State VARCHAR(2),
 PhoneNumber INT,
 Email VARCHAR(45),
 PRIMARY KEY(EmployeeID)
);

CREATE TABLE IF NOT EXISTS Invoice
(
 InvoiceID INT,
 CustomerID INT,
 Total DECIMAL(19,4),
 EmployeeID INT,
 PRIMARY KEY(InvoiceID),
 FOREIGN KEY(CustomerID) REFERENCES Customer(CustomerID),
 FOREIGN KEY(EmployeeID) REFERENCES Employee(EmployeeID)
);

CREATE TABLE IF NOT EXISTS InvoiceItem
(
 InvoiceItemID INT,
 InvoiceID INT,
 ComputerID INT,
 PRIMARY KEY(InvoiceItemID),
 FOREIGN KEY(InvoiceID) REFERENCES Invoice(InvoiceID),
 FOREIGN KEY(ComputerID) REFERENCES Computer(ComputerID)
);

INSERT INTO Brand
 (BrandID, BrandName)
VALUES
 (101, 'Toshiba'),
 (102, 'ASUS'),
 (103, 'Dell'),
 (104, 'Samsung'),
 (105, 'MSI'),
 (106, 'Apple');

INSERT INTO Model
 (ModelName, BrandID)
VALUES 
 ('Satellite L50D-BBT2N22', 101),
 ('Transformer Book T100TAF', 102),
 ('Inspiron 3000', 103),
 ('ATIV One 7 Curved', 104),
 ('GE60 2PE APACHE PRO', 105),
 ('Summer 2014 13 in. MacBook Pro', 106),
 ('Wind Box DC111', 105),
 ('Alienware 17', 103),
 ('ATIV Book 9 Plus', 104);

INSERT INTO Platform
 (PlatformID, Platform)
VALUES
 (001, 'Laptop'),
 (002, 'Desktop');

INSERT INTO Computer
 ( ComputerID, ModelName, Processor, Memory, HardDrive, OperatingSystem, PlatformID)
VALUES
 (178045, 'Satellite L50D-BBT2N22', 'AMD Quad-Core A4-6210', '4GB', '1TB', 'Windows 8.1', 001),
 (178046, 'Transformer Book T100TAF', 'Intel Bay Trail-T Quad Core Z3735 1.33 GHz', '2GB', '32GB', 'Windows 8.1', 001),
 (178047, 'Inspiron 3000', 'Intel Core i5-4460', '8GB', '1TB', 'Windows 8.1', 002),
 (178048, 'ATIV One 7 Curved', 'Intel Core i5 Processor 5200U', '8GB', '1TB', 'Windows 8.1', 002),
 (178049, 'GE60 2PE APACHE PRO', 'Intel Core i7 Processor', '16GB', '1TB', 'Windows 8.1', 001),
 (178050, 'Summer 2014 13 in. MacBook Pro', '2.5GHz dual-core Intel Core i5', '4GB', '500GB', 'OS X Yosemite', 001),
 (178051, 'Wind Box DC111', 'Intel Celeron Dual Core', '4GB', ' 500GB', 'Windows 8.1', 002),
 (178052, 'Alienware 17', 'Intel Core i7', '8GB', '1TB', 'WIndows 8.1', 001),
 (178053, 'ATIV Book 9 Plus', 'Intel Core i5', '8GB', '128GB', 'Windows 8.1', 001);

INSERT INTO Customer
 (CustomerID, LastName, FirstName, Address, Zip, City, State, PhoneNumber, Email)
VALUES
 (14670, 'Franks', 'Robert', '2905 North Ave.', 21218, 'Baltimore', 'MD', 443-875-9090, 'r.franks@gmail.com'),
 (14671, 'Smith', 'Anthony', '28 Rhodes Pl.', 21093, 'Lutherville-Timonium', 'MD', 410-252-6542, 'asmith@me.com'),
 (14672, 'Anderson', 'Mary', '1784 Cranbrook Dr.', 21093, 'Lutherville-Timonium', 'MD', 410-687-8235, 'm.anderson@comcast.net'),
 (14673, 'Keith', 'Toby', '987 Rodeo Dr.', 21093, 'Lutherville-Timonium', 'MD', 443-267-0900, 'not_that_toby.keith@gmail.com'),
 (14674, 'Karwacki', 'Ryan', '16200 Yeoho Rd', 21152, 'Hereford', 'MD', 410-350-4456, 'r.karwacki44@gmail.com'),
 (14675, 'Yancey', 'Marcus', '165 Twilight Ct.', 21218, 'Baltimore', 'MD', 443-908-9087, 'm.yancey35@aol.com');

INSERT INTO Employee
 (EmployeeID, Position, LastName, FirstName, Address, Zip, City, State, PhoneNumber, Email)
VALUES
 (100001, 'CEO', 'Brocato', 'Christopher', '26 Rhodes Pl.', 21093, 'Lutherville-Timonium', 'MD', 410-812-0548, 'c.brocat0@prestigeww.com'),
 (100893, 'Location Manager', 'White', 'Walter', '687 Winning Dr.', 21117, 'Owings Mills', 'MD', 410-674-8890, 'w.white@prestigeww.com'),
 (100894, 'Computer Engineer', 'Pinkman', 'Jesse', '15 Pot Spring Cr.', 21093, 'Lutherville-Timonium', 'MD', 443-897-5467, 'j.pinkman@prestigeww.com'),
 (100895, 'Computer Engineer', 'Fring', 'Gustavo', '8796 Westmister Br.', 21117, 'Owings Mills', 'MD', 443-098-1111, 'g.fring@prestigeww.com'),
 (100896, 'Software Specialist', 'Boetticher', 'Gale', '7845 Sunny Ln.', 21093, 'Lutherville-Timonium', 'MD', 443-896-5674, 'g.boetticher@prestigeww.com'),
 (100087, 'Lawyer', 'Goodman', 'Saul', '7823 Goodman Ln.', 21093, 'Lutherville-Timonium', 'MD', 410-657-8900, 's.goodman@prestigeww.com');

INSERT INTO Invoice
 (InvoiceID, Total, CustomerID, EmployeeID)
VALUES
 (237871, 115.99, 14670, 100893),
 (237872, 87.89, 14671, 100894),
 (237873, 476.95, 14672, 100895),
 (237874, 314.95, 14673, 100896),
 (237875, 45.96, 14674, 100001),
 (237876, 79.84, 14675, 100087);

INSERT INTO InvoiceItem
 (InvoiceItemID, InvoiceID, ComputerID)
VALUES
 (1008, 237871, 178045),
 (1009, 237872, 178046),
 (1010, 237873, 178047),
 (1011, 237874, 178048),
 (1012, 237875, 178049),
 (1013, 237876, 178050); 

任何帮助都将不胜感激

---

谢谢。

这应该可以完成以下工作：

SELECT *
FROM computer c

LEFT OUTER JOIN model m ON m.ModelName = c.ModelName
LEFT OUTER JOIN brand b ON b.BrandID = m.BrandID

您可能需要根据需要更改返回的字段。祝项目顺利

==更新-按照您的要求进行订购：

SELECT *
FROM brand b

LEFT OUTER JOIN model m ON m.BrandID = b.BrandID
LEFT OUTER JOIN computer c ON c.ModelName = m.ModelName

==第2次更新-包括新的“平台”表

SELECT *
FROM brand b

LEFT OUTER JOIN model m ON m.BrandID = b.BrandID
LEFT OUTER JOIN computer c ON c.ModelName = m.ModelName
LEFT OUTER JOIN platform p ON p.platformID = c.PlatformID

==第3次更新-上述内容涵盖了2、3和4个表的1-多个关系。要添加多对多关系，您可能需要查看计算机与发票的关系，因为计算机可以位于多个发票中，并且发票（在现实生活中）可以包含多个计算机。最初提出的数据结构不允许这样做。为InvoiceItem添加一个表可以实现这一点

计算机和发票之间的关系将是多对多[计算机（多）-（多）发票]这是通过在它们之间添加链接表来实现的：

Computer (1)-(Many) InvoiceItem (many)-(1) Invoice

==第四次更新 要实现这一点，请从发票表中删除computerID，并添加具有以下字段的新表InvoiceItem-InvoiceItemID、InvoiceNumber、computerID。然后从数据库检索发票项目的查询将是：

SELECT *
FROM Invoice i
LEFT OUTER JOIN InvoiceItem ii ON ii.InvoiceNumber = i.InvoiceNumber
LEFT OUTER JOIN Computer c ON c.computerID = ii.computerID

您可以将其扩展为还包括其他与计算机相关的表，包括：

SELECT *
FROM Invoice i
LEFT OUTER JOIN InvoiceItem ii ON ii.InvoiceNumber = i.InvoiceNumber
LEFT OUTER JOIN Computer c ON c.computerID = ii.computerID
LEFT OUTER JOIN Model m ON m.ModelName = c.ModelName
LEFT OUTER JOIN Brand b ON b.BrandID = m.BrandID
LEFT OUTER JOIN platform p ON p.platformID = c.PlatformID

---

如果我真的很挑剔，我会放弃名称上的链接，只要使用ID，如果模型名称稍有更改，查询将不再工作。使用纯粹的IDs可以避免这种情况。

您要将哪些表连接在一起？我试图连接品牌、型号和计算机，但想不通。好的，非常感谢，为了确保这是一对多的关系…1品牌->多型号->多台计算机。。如果您喜欢从品牌b左外连接m上的型号m中选择*，则可以重新写入。BrandID=b.BrandID左外连接c上的计算机c.ModelName=m.ModelName如果您添加另一台使用同一型号的计算机，则该型号将显示两次，每台使用该型号的计算机显示一次。将另一个模型添加到一个品牌，并为此添加一台计算机，该品牌将显示多次。您当前的数据没有任何东西来说明一对多的关系好吧，我从您那里得到的是，到目前为止，我只有一对一的关系。因此，如果我要为每个品牌添加多个型号，这将使其成为一对多关系。数据库关系是一对多关系，但您的数据没有说明这一点，所以是的：）为每个品牌添加另一个型号或为每个型号添加计算机将突出这一点。还有什么问题，就问：）