SQL数据库中的外键问题

Question

I have a school assignment that that is giving me and my friends headaches... So this is my queries that i have executed, one at a time ofc...

CREATE DATABASE GamblingSociety;

USE GamblingSociety;

CREATE TABLE GamblingDen
(
    Name VARCHAR (20) PRIMARY KEY,
    Address VARCHAR (50),
    Phone VARCHAR (10)
);

CREATE TABLE Room (
    RoomNr INT,
    GameCapaity INT,
    GamblingDenName VARCHAR (20),
    PRIMARY KEY (RoomNr, GamblingDenName),
    FOREIGN KEY (GamblingDenName) REFERENCES GamblingDen (Name)
);

CREATE TABLE Employee (
    SSN CHAR (11) PRIMARY KEY,
    Name VARCHAR (20),
    Address VARCHAR(50),
    Salary INT,
    isBoss BOOL,
    GamblingDenName VARCHAR (20),
    FOREIGN KEY (GamblingDenName) REFERENCES GamblingDen (Name)
);

CREATE TABLE GameType (
    Name VARCHAR (20) PRIMARY KEY,
    WinningProcentage FLOAT,
    ResponsibleEmployee CHAR (11),
    FOREIGN KEY (ResponsibleEmployee) REFERENCES Employee (SSN)
);

CREATE TABLE Supplier (
    Name VARCHAR (20) PRIMARY KEY,
    Address VARCHAR (50)
);

CREATE TABLE SupplierOfGameType (
    SupplierName VARCHAR (20),
    GameTypeName VARCHAR (20),
    PRIMARY KEY(SupplierName, GameTypeName),
    FOREIGN KEY (SupplierName) REFERENCES Supplier (Name),
    FOREIGN KEY (GameTypeName) REFERENCES GameType (Name)
);

CREATE TABLE GamblingTable (
    TableNr INT,
    RoomNr INT,
    GamblingDenName VARCHAR (20),
    GameTypeName VARCHAR (20),
    Comments VARCHAR (128),
    PRIMARY KEY (RoomNr, TableNr, GamblingDenName, GameTypeName),
    FOREIGN KEY (RoomNr, GamblingDenName) REFERENCES Room (RoomNr, GamblingDenName),
    FOREIGN KEY (GameTypeName) REFERENCES GameType (Name)
);

CREATE TABLE Shylock (
    Phone CHAR (10) PRIMARY KEY,
    Name VARCHAR (20),
    Contry CHAR (3)
);

CREATE TABLE Customer (
    SSN CHAR (11) PRIMARY KEY,
    Name VARCHAR (20),
    Phone CHAR (10),
    Address VARCHAR (50)
);

But this last query does not work:

USE GamblingSociety;

CREATE TABLE GamblingInstance (
    StartTime DATETIME,
    EndingTime DATETIME,
    GamblingDenName VARCHAR (20),
    TableNr INT, 
    GameTypeName VARCHAR (20), 
    Customer CHAR (11),
    Shylock CHAR (10), 
    Debt INT, 
    DebtPayed BOOL,
    DebtPayedDate DATETIME,
    PRIMARY KEY (StartTime, GameTypeName, Customer),
    FOREIGN KEY (GamblingDenName, TableNr, GameTypeName) REFERENCES GamblingTable (GamblingDenName, TableNr, GameTypeName),
    FOREIGN KEY (Customer) REFERENCES Customer (SSN),
    FOREIGN KEY (Shylock) REFERENCES Shylock (Phone)
);

It gives me this error: "Error Code: 1005. Can't create table 'gamblingsociety.gamblinginstance' (errno: 150)"

if I replace this:

FOREIGN KEY (GamblingDenName, TableNr, GameTypeName) REFERENCES GamblingTable (GamblingDenName, TableNr, GameTypeName),

with this:

FOREIGN KEY (GameTypeName) REFERENCES GamblingTable (GameTypeName),

It works, so it's something with the GamblingDenName and TableNr.

And i have google it and found a lot of tips, but nothing yeat have worked...

So anyone with any idea?

Thanks in advance!

Answer 1

There is no key in GamblingTable that can satisfy this REFERENCE:

  REFERENCES GamblingTable (GamblingDenName, TableNr, GameTypeName),

That is, there is no key in GamblingTable for which GamblingDenName, TableNr, GameTypeName are the only columns, or the first three columns.

There is a key that satisfies REFERENCES GamblingTable (GameTypeName) , which is why that version works.

(I have to say that I've never actually seen FOREIGN KEYs being used to parent other FOREIGN KEYs, but I guess it works).