php - array_unique が誤って値を破棄する

Question

array_unique を使用して、繰り返される値を破棄しようとしています。

Array
(
    [0] => Array
        (
            [book_id] => 1203910329
            [author] => Gauci, Joe
            [description] => Paperback. Very Good.
            [isbn] => 9781907374067
            [publisher] =>
            [date] =>
            [currency] => USD
            [price] => 10.97
            [bookseller] => xx
            [bookseller_location] => GBR
            [condition] => 3
            [shipping_ground] => 4.73
            [shipping_expedited] => 6.33
        )

    [1] => Array
        (
            [book_id] => 12312314556
            [author] => Gauci, Joe
            [description] => Paperback. GOOD.
            [isbn] => 9781907374067
            [publisher] =>
            [date] =>
            [currency] => USD
            [price] => 1.84
            [bookseller] => xx
            [bookseller_location] => GBR
            [condition] => 2.5
            [shipping_ground] => 4.73
            [shipping_expedited] => 6.33
        )

    [2] => Array
        (
            [book_id] => 12312314556
            [author] => Gauci, Joe
            [description] => Paperback. GOOD.
            [isbn] => 9781907374067
            [publisher] =>
            [date] =>
            [currency] => USD
            [price] => 1.84
            [bookseller] => xx
            [bookseller_location] => GBR
            [condition] => 2.5
            [shipping_ground] => 4.73
            [shipping_expedited] => 6.33
        )

)

array_unique($results)最初の値のみを使用するたびに返されます

 Array
    (
        [0] => Array
            (
                [book_id] => 1203910329
                [author] => Gauci, Joe
                [description] => Paperback. Very Good.
                [isbn] => 9781907374067
                [publisher] =>
                [date] =>
                [currency] => USD
                [price] => 10.97
                [bookseller] => xx
                [bookseller_location] => GBR
                [condition] => 3
                [shipping_ground] => 4.73
                [shipping_expedited] => 6.33
            )
    )

どこに行くのarray_unique？