Şöyle bir şey olabilir :
MySQL için :
CREATE TABLE User
(
id
int NOT NULL AUTO_INCREMENT,
name
varchar(100) NOT NULL,
PRIMARY KEY (id
)
)
CREATE TABLE Friend
(
friendId1
int NOT NULL,
friendId2
int NOT NULL,
KEY Friend_User_FK
(friendId1
),
KEY Friend_User_FK_1
(friendId2
),
CONSTRAINT Friend_User_FK
FOREIGN KEY (friendId1
) REFERENCES User
(id
),
CONSTRAINT Friend_User_FK_1
FOREIGN KEY (friendId2
) REFERENCES User
(id
)
)