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我不断收到以下错误在SQL代码中找不到多个级联路径或循环的位置？
消息1785，级别16，状态0，99号线 上表>“linkUserGroup”可能会导致循环或多个级联路径引进国外KEY约束“FK_linkUserGroup_tblStudent”。指定ON DELETE？> NO ACTION或ON UPDATE NO ACTION，或修改其他FOREIGN KEY约束。 消息1750，级别16，状态0，行99 无法创建约束或索引。查看以前的错误。
我不明白如何循环或多个级联路径是可能的？我也无法理解FK对TeacherID的限制如何导致同样的问题？我的理解是，如果要删除父StudentID，那么通过指定子表中的On Delete No Action应确保该记录不会从子表中删除。我不明白他们有什么其他途径或可能的循环？请帮助
CREATE TABLE tblUserAccount (
uaUserAccountID INT IDENTITY (1,1) CONSTRAINT PK_tblUserAccount PRIMARY KEY CLUSTERED,
uaUserAccountTitle NVARCHAR (50) NOT NULL,
uaUserAccountFirstName NVARCHAR (50) NOT NULL,
uaUserAccountSurname NVARCHAR (50) NOT NULL,
uaUserAccountUserName NVARCHAR (50) NOT NULL,
uaUserAccountPassword NVARCHAR (50) NOT NULL,
uaDateTimeModified DATETIME
CONSTRAINT DF_tblUserAccount_DateTimeModified DEFAULT SYSDATETIME()
);
CREATE TABLE tblRole (
rRoleID INT IDENTITY (1, 1) CONSTRAINT PK_tblRole PRIMARY KEY CLUSTERED,
rRole NVARCHAR (50),
rRoleDescription NVARCHAR (MAX) NULL,
rDateTimeModified DATETIME
CONSTRAINT DF_tblRole_DateTimeModified DEFAULT SYSDATETIME()
);
CREATE TABLE linkUserAccountRole (
uarUserAccountID INT,
uarRoleID INT,
uarDateTimeModified DATETIME
CONSTRAINT DF_linkUserAccountRole_DateTimeModified DEFAULT SYSDATETIME()
,CONSTRAINT PK_linkUserAcccountRole
PRIMARY KEY CLUSTERED (uarUserAccountID , uarRoleID)
,CONSTRAINT FK_linkUserAcccountRole_tblRole
FOREIGN KEY (uarRoleID)
REFERENCES tblRole (rRoleID)
ON DELETE NO ACTION
ON UPDATE CASCADE
,CONSTRAINT FK_linkUserAcccountRole_tblUserAccount
FOREIGN KEY (uarUserAccountID)
REFERENCES tblUserAccount (uaUserAccountID)
ON DELETE NO ACTION
ON UPDATE CASCADE
);
CREATE TABLE tblTeacher (
tTeacherID INT CONSTRAINT PK_tblTeacher PRIMARY KEY CLUSTERED,
tUserAccountID INT,
tDateTimeModified DATETIME
CONSTRAINT DF_tblTeacher_DateTimeModified DEFAULT SYSDATETIME(),
CONSTRAINT FK_tblTeacher_tblUserAccount
FOREIGN KEY (tUserAccountID)
REFERENCES tblUserAccount(uaUserAccountID)
ON DELETE CASCADE
ON UPDATE CASCADE
);
CREATE TABLE tblStudent (
sStudentID INT CONSTRAINT PK_tblStudent PRIMARY KEY CLUSTERED,
sUserAccountID INT,
sDateTimeModified DATETIME
CONSTRAINT DF_tblStudent_DateTimeModified DEFAULT SYSDATETIME(),
CONSTRAINT FK_tblStudent_tblUserAccount
FOREIGN KEY (sUserAccountID)
REFERENCES tblUserAccount(uaUserAccountID)
ON DELETE CASCADE
ON UPDATE CASCADE
);
CREATE TABLE tblKeyStage (
ksKeyStageGroupID INT IDENTITY (1,1) CONSTRAINT PK_tblKeyStage PRIMARY KEY CLUSTERED,
ksKeyStageTitle NVARCHAR (50) NOT NULL,
ksKeyStageDescription NVARCHAR(50),
ksDateTimeModified DATETIME
CONSTRAINT DF_tblKeyStage_DateTimeModified DEFAULT SYSDATETIME()
,CONSTRAINT UQ_tblKeyStage_KeyStageTitle UNIQUE (ksKeyStageTitle)
);
CREATE TABLE tblYearGroup (
ygYearGroupID INT IDENTITY (1,1) CONSTRAINT PK_tblYearGroup PRIMARY KEY CLUSTERED,
ygYearGroupTitle NVARCHAR (50) NOT NULL,
ygYearGroupDescription NVARCHAR(50),
ygDateTimeModified DATETIME
CONSTRAINT DF_tblYearGroup_DateTimeModified DEFAULT SYSDATETIME()
,CONSTRAINT UQ_tblYearGroup_YearGroupTitle UNIQUE (ygYearGroupTitle)
);
CREATE TABLE tblClassGroup (
cgClassGroupID INT IDENTITY (1,1) CONSTRAINT PK_tblClassGroup PRIMARY KEY CLUSTERED,
cgClassGroupTitle NVARCHAR (50) NOT NULL,
cgClassGroupDescription NVARCHAR (50),
cgDateTimeModified DATETIME
CONSTRAINT DF_tblClassGroup_DateTimeModified DEFAULT SYSDATETIME()
,CONSTRAINT UQ_tblClassGroup_ClassGroupTitle UNIQUE (cgClassGroupTitle)
);
CREATE TABLE tblLearningGroup (
lgLearningGroupID INT IDENTITY (1,1) CONSTRAINT PK_tblLearningGroup PRIMARY KEY CLUSTERED,
lgLearningGroupTitle NVARCHAR (50) NOT NULL,
lgLearningGroupDescription NVARCHAR (50),
lgDateTimeModified DATETIME
CONSTRAINT DF_tblLearningGroup_DateTimeModified DEFAULT SYSDATETIME()
,CONSTRAINT UQ_tblLearningGroup_LearningGroupTitle UNIQUE (lgLearningGroupTitle)
);
CREATE TABLE tblLearningGroup (
lgLearningGroupID INT IDENTITY (1,1) CONSTRAINT PK_tblLearningGroup PRIMARY KEY CLUSTERED,
lgLearningGroupTitle NVARCHAR (50) NOT NULL,
lgLearningGroupDescription NVARCHAR (50),
lgDateTimeModified DATETIME
CONSTRAINT DF_tblLearningGroup_DateTimeModified DEFAULT SYSDATETIME()
,CONSTRAINT UQ_tblLearningGroup_LearningGroupTitle UNIQUE (lgLearningGroupTitle)
);
CREATE TABLE linkUserGroup (
ugTeacherID INT,
ugStudentID INT,
ugKeyStageGroupID INT,
ugYearGroupID INT,
ugClassGroupID INT,
ugLearningGroupID INT,
ugDateTimeModified DATETIME
CONSTRAINT DF_linkUserGroup_DateTimeModified DEFAULT SYSDATETIME()
,CONSTRAINT PK_linkUserGroup
PRIMARY KEY CLUSTERED (ugTeacherID, ugStudentID, ugClassGroupID, ugLearningGroupID)
,CONSTRAINT FK_linkUserGroup_tblTeacher
FOREIGN KEY (ugTeacherID)
REFERENCES tblTeacher (tTeacherID)
ON DELETE NO ACTION
ON UPDATE CASCADE
,CONSTRAINT FK_linkUserGroup_tblStudent
FOREIGN KEY (ugStudentID)
REFERENCES tblStudent (sStudentID)
ON DELETE NO ACTION
ON UPDATE CASCADE
,CONSTRAINT FK_linkUserGroup_tblKeyStage
FOREIGN KEY (ugKeyStageGroupID)
REFERENCES tblKeyStage (ksKeyStageGroupID)
ON DELETE NO ACTION
ON UPDATE CASCADE
,CONSTRAINT FK_linkUserGroup_tblYearGroup
FOREIGN KEY (ugYearGroupID)
REFERENCES tblYearGroup (ygYearGroupID)
ON DELETE NO ACTION
ON UPDATE CASCADE
,CONSTRAINT FK_linkUserGroup_tblClassGroup
FOREIGN KEY (ugClassGroupID)
REFERENCES tblClassGroup (cgClassGroupID)
ON DELETE NO ACTION
ON UPDATE CASCADE
,CONSTRAINT FK_linkUserGroup_tblLearningGroup
FOREIGN KEY (ugLearningGroupID)
REFERENCES tblLearningGroup (lgLearningGroupID)
ON DELETE NO ACTION
ON UPDATE CASCADE
,CONSTRAINT UQ_linkUserGroup_PK_YearGroupID
UNIQUE (ugTeacherID, ugStudentID, ugClassGroupID, ugLearningGroupID, ugYearGroupID)
);
