使用复合主键作为外键

小编典典

使用复合主键作为外键

mysql

如何使用复合主键作为外键？看来我的尝试无效。

create table student
(
student_id varchar (25) not null ,
student_name varchar (50) not null ,
student_pone int ,
student_CNIC varchar (50),
students_Email varchar (50),
srudents_address varchar(250),
dept_id varchar(6),
batch_id varchar(4),
FOREIGN KEY (dept_id) REFERENCES department(dept_id),
FOREIGN KEY (batch_id) REFERENCES batch(batch_id),
CONSTRAINT pk_studentID PRIMARY KEY (batch_id,dept_id,student_id) )

create table files
(
files_name varchar(50) not null ,
files_path varchar(50),
files_data varchar(max),
files_bookmarks xml ,
FOREIGN KEY (pk_studentID ) REFERENCES student(pk_studentID ),
CONSTRAINT pk_filesName PRIMARY KEY (files_name) )

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2020-05-17

共1个答案

小编典典

该行：

FOREIGN KEY (pk_studentID ) REFERENCES student(pk_studentID ),

是错的。您不能那样使用pk_studentID，这只是父表中PK约束的名称。要将复合主键用作外键，您必须向子表中添加相同数量（组成PK）的相同数据类型的列，然后在FOREIGN KEY定义中使用这些列的组合：

CREATE TABLE files
(
  files_name varchar(50) NOT NULL,

  batch_id varchar(4) NOT NULL,         --- added, these 3 should not
  dept_id varchar(6) NOT NULL,          --- necessarily be NOT NULL
  student_id varchar (25) NOT NULL,     ---

  files_path varchar(50),
  files_data varchar(max),              --- varchar(max) ??   
  files_bookmarks xml,                  --- xml ??
                                        --- your question is tagged MySQL, 
                                        --- and not SQL-Server

  CONSTRAINT pk_filesName 
    PRIMARY KEY (files_name),

  CONSTRAINT fk_student_files                     --- constraint name (optional)
    FOREIGN KEY (batch_id, dept_id, student_id)  
      REFERENCES student (batch_id, dept_id, student_id)
) ENGINE = InnoDB ;

2020-05-17