Hello Reader's! if you have an given array on with you want to sort with any selected key index as show below:-

Array
        (
            [0] => Array
                (
                    [configuration_id] => 10
                    [id] => 1
                    [optionNumber] => 3
                    [optionActive] => 1
                    [lastUpdated] => 2010-03-17 15:44:12
                )

            [1] => Array
                (
                    [configuration_id] => 9
                    [id] => 1
                    [optionNumber] => 2
                    [optionActive] => 1
                    [lastUpdated] => 2010-03-17 15:44:12
                )

            [2] => Array
                (
                    [configuration_id] => 8
                    [id] => 1
                    [optionNumber] => 1
                    [optionActive] => 1
                    [lastUpdated] => 2010-03-17 15:44:12
                )
    )

And you want your array to be like this:-

 Array
            (
                [0] => Array
                    (
                        [configuration_id] => 8
                        [id] => 1
                        [optionNumber] => 1
                        [optionActive] => 1
                        [lastUpdated] => 2010-03-17 15:44:12
                    )

                [1] => Array
                    (
                        [configuration_id] => 9
                        [id] => 1
                        [optionNumber] => 2
                        [optionActive] => 1
                        [lastUpdated] => 2010-03-17 15:44:12
                    )

                [2] => Array
                    (
                        [configuration_id] => 10
                        [id] => 1
                        [optionNumber] => 3
                        [optionActive] => 1
                        [lastUpdated] => 2010-03-17 15:44:12
                    )
        )

Now you have to use the code as written below:-

function cmp_by_optionNumber($a, $b) {
  return $a["optionNumber"] - $b["optionNumber"];
}

usort($array, "cmp_by_optionNumber");