Probléme création Table avec clef étrangère

Bonjour,

Quand je crée cette table tous ce passe bien :

CREATE TABLE informations (
Id int(10) unsigned NOT NULL AUTO_INCREMENT,
Id_Campagne int(10) unsigned NOT NULL,
Date timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
MesurePression float unsigned NOT NULL,
MesureDebit float unsigned NOT NULL,
Mode tinyint(3) unsigned NOT NULL,
ConsigneDebit float unsigned NOT NULL,
ConsignePression float unsigned NOT NULL,
VitesseRotation float unsigned NOT NULL,
Frequence float unsigned NOT NULL,
Puissance float unsigned NOT NULL,
Tension float unsigned NOT NULL,
Courant float unsigned NOT NULL,
PRIMARY KEY (Id)
) ENGINE=InnoDB


Mais quand je crée celle ci un message d'erreur s'affiche

CREATE TABLE campagnes (
Id_informations int(10) unsigned NOT NULL,
Id int(10) unsigned NOT NULL AUTO_INCREMENT,
Nom char(20) NOT NULL,
INDEX inf_id (Id_informations),
FOREIGN KEY (Id_informations) REFERENCES informations(Id)
ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB

ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it
must be defined as a key

Merci de votre aide.