MySQL：无法添加foriegn键约束

Question

以下是2个表格。错误出现在表“Medical_Record”的最后两行：

CREATE TABLE Medical_Record(
Patient_SSN VARCHAR(10),
Record_ID VARCHAR(10),
Medical_Issue VARCHAR(45),
Medical_Status VARCHAR(15),
Doctor_ID VARCHAR(10),
Hosp_ID VARCHAR(10),
Event_Date DATE,
PRIMARY KEY (Patient_SSN,Record_ID),
FOREIGN KEY (Patient_SSN) REFERENCES Citizen(SSN) ON DELETE CASCADE ON UPDATE CASCADE,
FOREIGN KEY (Doctor_ID,Hosp_ID) REFERENCES Employment_Status(Worker_ID) ON DELETE CASCADE ON UPDATE CASCADE,
);

CREATE TABLE Employment_Status(
Citizen_SSN VARCHAR(10),
Worker_ID VARCHAR(10),
Org_ID VARCHAR(10),
Employee_Position VARCHAR(15),
Join_Date DATE,
Leave_Date DATE,
Profession VARCHAR(30),
PRIMARY KEY (Citizen_SSN,Worker_ID,Org_ID),
FOREIGN KEY (Citizen_SSN) REFERENCES Citizen(SSN) ON DELETE CASCADE ON UPDATE CASCADE,
FOREIGN KEY (Org_ID) REFERENCES Organization(Org_ID) ON DELETE CASCADE ON UPDATE CASCADE
);

CREATE TABLE Citizen(
SSN VARCHAR(10),
FName VARCHAR(15),
MName VARCHAR(15),
LName VARCHAR(15),
Gender VARCHAR(1),
Birth_Date DATE,
Death_Date DATE,
Spouse_SSN VARCHAR(10),
Blood_Group VARCHAR(5),
Pincode VARCHAR(7),
Address TEXT,
PRIMARY KEY (SSN),
FOREIGN KEY (Spouse_SSN) REFERENCES Citizen(SSN) ON DELETE CASCADE ON UPDATE CASCADE
);

CREATE TABLE Organization(
Org_ID VARCHAR(10),
Org_Name VARCHAR(45),
Email VARCHAR(45),
Phone_Number VARCHAR(15),
Established_Date DATE,
Closing_Date DATE,
PRIMARY KEY (Org_ID)
);

Answer 1

<强> UPDATE1 ：
下面是执行sql脚本的实际错误。

您在Employee_Status表中定义了一个复合键 每列定义单个键，然后在子表中引用 它应该工作。

PRIMARY KEY (Citizen_SSN,Worker_ID,Org_ID),
KEY (Worker_ID),  -- <-------- Add this line
KEY (Org_ID),  -- <-------- Add this line

原始答案：
每个引用的父字段都必须在其上定义index。这是外键添加的条件。

根据外键约束的文档：

REFERENCES parent_tbl_name (index_col_name,...)

在列Employment_Status.Worker_ID和Employment_Status.Org_ID上定义相关的键。那么你应该能够在子表中引用它们。

请参阅：

• MySQL Using FOREIGN KEY Constraints

  

[CONSTRAINT [symbol]] FOREIGN KEY
      [index_name]（index_col_name，...）
      参考文献tbl_name（index_col_name，...）
      [ON DELETE reference_option]
      [ON UPDATE reference_option]

     

reference_option：
      限制| CASCADE | SET NULL |没有行动