SQL Server 2014中的外键错误

Question

抱歉，我在这里必须更具体。 因此，以下是SQL我的代码。 复制并粘贴到SQL中。 基本上，我正在创建链接在一起的13个表。

IF EXISTS (SELECT*FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME='EventType')
BEGIN
    DROP TABLE EventType
END
GO

IF EXISTS (SELECT*FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME='EventLocation')
BEGIN
    DROP TABLE EventLocation
END
GO

IF EXISTS (SELECT*FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME='StudentEvent')
BEGIN
    DROP TABLE StudentEvent
END
GO

IF EXISTS (SELECT*FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME='Event')
BEGIN
    DROP TABLE Event
END
GO

IF EXISTS (SELECT*FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME='CurrentAddress')
BEGIN
    DROP TABLE CurrentAddress
END
GO

IF EXISTS (SELECT*FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME='PreviousAddress')
BEGIN
    DROP TABLE PreviousAddress
END
GO

IF EXISTS (SELECT*FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME='ContactType')
BEGIN
    DROP TABLE ContactType
END
GO

IF EXISTS (SELECT*FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME='Contact')
BEGIN
    DROP TABLE Contact
END
GO

IF EXISTS (SELECT*FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME='StudentMajor')
BEGIN
    DROP TABLE StudentMajor
END
GO

IF EXISTS (SELECT*FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME='Major')
BEGIN
    DROP TABLE Major
END
GO

IF EXISTS (SELECT*FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME='Citizenship')
BEGIN
    DROP TABLE Citizenship
END
GO

IF EXISTS (SELECT*FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME='Country')
BEGIN
    DROP TABLE Country
END

IF EXISTS (SELECT*FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME='Student')
BEGIN
    DROP TABLE Student
END
GO

CREATE TABLE Student
(
    StudentID int identity PRIMARY KEY,
    FirstName varchar (50),
    LastName varchar (30)
)
GO

CREATE TABLE Country
(
    CountryID int identity PRIMARY KEY,
    CountryOfBirth varchar (10),
    StudentID int FOREIGN KEY REFERENCES Student(StudentID)
)
GO

CREATE TABLE Citizenship
(
    CitizenshipID int identity PRIMARY KEY,
    CountryOfCitizenship1 varchar (10),
    CountryOfCitizenship2 varchar (10),
    StudentID int FOREIGN KEY REFERENCES Student(StudentID),
    CountryID int FOREIGN KEY REFERENCES Country(CountryID)
)
GO

CREATE TABLE Major
(
    Majorid int identity PRIMARY KEY,
    MajorName varchar(30),
    GraduatedMajor varchar (30)
)

CREATE TABLE StudentMajor
(
    StudentMajorid int identity,
    StudentID int FOREIGN KEY REFERENCES Student(StudentID),
    MajorID int FOREIGN KEY REFERENCES Major(MajorID)
)
GO

ALTER TABLE StudentMajor
   ADD constraint uk_sm UNIQUE (StudentID,MajorID)

 CREATE TABLE Contact 
 (
    ContactId int identity PRIMARY KEY,
    StudentID int FOREIGN KEY REFERENCES Student(StudentID),
    ContactInfo varchar (8),
    ContactDate datetime
)
GO

CREATE TABLE ContactType
(
    ContactTypeId int identity PRIMARY KEY,
    ContactID int FOREIGN KEY REFERENCES Contact(ContactID)
)
GO

CREATE TABLE PreviousAddress
(
    PreviousAddressId int identity PRIMARY KEY,
    Address1  varchar (50),
    Address2 varchar (50),
    City varchar (20),
    State varchar (20),
    Pincode char (10),
    StudentID int FOREIGN KEY REFERENCES Student(StudentID)
)
GO

CREATE TABLE CurrentAddress
(
    CurrentAddressId int identity PRIMARY KEY,
    Address1  varchar (50),
    Address2 varchar (50),
    City varchar (20),
    State varchar (20),
    Pincode char (10),
    StudentID int FOREIGN KEY REFERENCES Student(StudentID)
)
GO

CREATE TABLE EventType
(
    EventTypeID int identity PRIMARY KEY
)

CREATE TABLE Event
(
    EventId int identity PRIMARY KEY,
    EventDate  datetime,
    EventTitle varchar (50),
    EventTime datetime,
    EventTypeID int
)
GO

ALTER TABLE Event
    ADD constraint fk_Event 
        FOREIGN KEY (EventTypeID) REFERENCES EventType(EventTypeID)

CREATE TABLE StudentEvent
(
    StudentEventId int identity PRIMARY KEY,
    StudentID int FOREIGN KEY REFERENCES Student(StudentID),
    EventID int FOREIGN KEY REFERENCES Event(EventID),
    Comment varchar(2000)
)
GO

CREATE TABLE EventLocation 
(
    EventLocationId int identity PRIMARY KEY,
    EventCountry varchar (50),
    EventState varchar (50),
    EventAddress1  varchar (100),
    EventAddress2 varchar (100),
    EventCity varchar (50),
    EventPincode char (10),
    EventID int FOREIGN KEY REFERENCES Event(EventID)
)
GO

现在，上述代码的问题在于它将在第一次执行时完美执行，但是当我第二次执行时，它将引发以下错误。

无法删除对象“ EventType”，因为它是由FOREIGN KEY约束引用的。

讯息2714，第16级，州立6，第132行
数据库中已经有一个名为“ EventType”的对象。

Msg 4902，第16级，状态1，第143行
无法找到对象“事件”，因为它不存在或您没有权限。

消息1767，级别16，状态0，第153行
外键'FK__EventLoca__Event__6265874F'引用无效的表'Event'。 消息1750，级别16，状态0，第153行

无法创建约束或索引。 请参阅先前的错误。

有没有更好的方法来编码外键，或者我做错了什么。

在此先感谢您的帮助！

Answer 1

您应该首先创建表：

CREATE TABLE Event
(
    EventId int identity PRIMARY KEY,
    EventDate datetime,
    EventTitle varchar (50),
    EventTime datetime,
    EventTypeID int
)
GO

CREATE TABLE EventType
(
    EventTypeID int identity PRIMARY KEY
);

ALTER TABLE Event
    ADD constraint fk_Event 
        FOREIGN KEY (EventTypeID) REFERENCES EventType(EventTypeID);

或者，您可以将表创建为：

CREATE TABLE EventType
(
    EventTypeID int identity PRIMARY KEY
);

CREATE TABLE Event
(
    EventId int identity PRIMARY KEY,
    EventDate datetime,
    EventTitle varchar (50),
    EventTime datetime,
    EventTypeID int,
    constraint fk_Event FOREIGN KEY (EventTypeID) REFERENCES EventType(EventTypeID)
);

更新：

无法删除对象“ EventType”，因为它是由FOREIGN KEY约束引用的。 消息2714，级别16，状态6，行132数据库中已经有一个名为“ EventType”的对象。 消息4902，级别16，状态1，行143找不到对象“事件”，因为它不存在或您没有权限。 消息1767，级别16，状态0，第153行外键'FK__EventLoca__Event__6265874F'引用了无效的表'Event'。 消息1750，级别16，状态0，第153行无法创建约束或索引。 请参阅先前的错误。

此错误消息很明显，您无法删除另一个表中引用的表，因此必须首先删除Event表，然后才能删除EventsType表。

Answer 2

尝试创建表EventType之前，先将其用作表Event的引用。