在php中按时间排序数组的问题

---array $points----

---数组$积分----

Array
    (
        [0] => Array
            (
                [0] => 2011-10-02 05:30:00
                [1] => 20
            )

        [1] => Array
            (
                [0] => 2011-10-04 09:30:00
                [1] => 12
            )

        [2] => Array
            (
                [0] => 2011-10-01 13:30:00
                [1] => 25
            )

        [3] => Array
            (
                [0] => 2011-10-03 02:30:00
                [1] => 31
            )

    )
Array