Добавление внешнего ключа на несколько столбцов

Question

Я пытаюсь создать внешний ключ на двух столбцах таблицы, чтобы указать на тот же столбец другой таблицы, но я, кажется, получаю ошибку ...

Вот что я делаю:

CREATE TABLE test2 (
  ID INT NOT NULL AUTO_INCREMENT,  
  col1 INT NOT NULL,
  col2 INT NOT NULL, 
  PRIMARY KEY (ID),
  CONSTRAINT fk FOREIGN KEY (col1, col2)
                REFERENCES test1(ID, ID)
  ON UPDATE CASCADE
  ON DELETE RESTRICT
) ENGINE=InnoDB;

.

Но я получаю

ERROR 1005 (HY000): Can't create table 'DB.test2' (errno: 150)

Если у меня есть только один столбец, однако, таблица правильно создана.

Может ли кто-нибудь указать мне, где ошибка?

спасибо n

Answer 1

Tried it here and got the same error. This works though:

CREATE TABLE test2 (
  ID INT NOT NULL AUTO_INCREMENT,  
  col1 INT NOT NULL,
  col2 INT NOT NULL, 
  PRIMARY KEY (ID),
  CONSTRAINT fk FOREIGN KEY (col1)
                REFERENCES test1(ID)
  ON UPDATE CASCADE
  ON DELETE RESTRICT,
  CONSTRAINT fk2 FOREIGN KEY (col2)
                REFERENCES test1(ID)
  ON UPDATE CASCADE
  ON DELETE RESTRICT

) ENGINE=InnoDB

Yes, I know - your script should work (even if it doesn't seem to make much sense). Yet, I guess this new version is better.

Answer 2

The problem would appear to be that you are specifying the same parent column twice in the same foreign key (i.e, (ID, ID)). The following should work:

Create Table Test1
    (
    PK1 int not null
    , PK2 int not null
    , Primary Key ( PK1, PK2 )
    )

Create Table Test2
    (
    Id int not null Auto_Increment
    , PK1 int not null
    , PK2 int not null
    , Primary Key ( ID )
    , Constraint FK_Test2
        Foreign Key ( PK1, PK2 )
        References Test1( PK1, PK2 )
    )

If it is the case, that you want two columns in a child table referencing the same parent table column, then you must add two foreign key references as shown by rsenna as those represent two independent relations.