Aggiunta di chiave esterna su più colonne

Question

Sto cercando di creare una chiave straniera su due colonne di una tabella per puntare alla stessa colonna di un'altra tabella, ma mi sembra di ottenere un errore ...

Ecco cosa faccio:

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;

.

Ma ottengo

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

Se ho solo una colonna, tuttavia, la tabella è creata correttamente.

Qualcuno potrebbe indicarmi da me dove è l'errore?

Grazie 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.