novice: table design FOREIGN key

["tony yau" <tony.yau@xxxxxxxxxxxx>]

Hi All

    Thanks for all your comments on my previous mail, very much appreciated.
I'm stuck again!
    I've created the following lookup table for m <-> m relationship between
a Group and a Contact table.

CREATE TABLE Group_Contact(
  GroupID INT NOT NULL,
  ContactID INT NOT NULL,

  Index (GroupID),
  FOREIGN KEY (GroupID) REFERENCES Group (PKey) ON DELETE CASCADE,
  Index (ContactID),
  FOREIGN KEY (ContactID) REFERENCES Contact (PKey) ON DELETE CASCADE
) TYPE=InnoDB COMMENT='Group to Contact lookup';

what do I need to do to ensure only unique (GroupID,ContactID) pair can be
inserted into the table?

Thanks
Tony Yau

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