MySQL 使用复合主键作为外键
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Use Composite Primary Key as Foreign Key
提问by comsian
How can I use a composite primary key as a foreign key? It looks like my attempt does not work.
如何使用复合主键作为外键？看起来我的尝试不起作用。
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) )
回答by ypercube??
The line:
线路：
FOREIGN KEY (pk_studentID ) REFERENCES student(pk_studentID ),
is wrong. You can't use pk_studentIDlike that, this is just the name of the PK constraint in the parent table. To use a compound Primary Key as Foreign Key, you'll have to add the same number of columns (that compose the PK) with same datatypes to the child table and then use the combination of these columns in the FOREIGN KEYdefinition:
是错的。你不能那样使用pk_studentID，这只是父表中 PK 约束的名称。要将复合主键用作外键，您必须将具有相同数据类型的相同数量的列（组成 PK）添加到子表中，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 ;
