//二维数组，按照里面的age从大到小降序，代码如下

<?php

header('Content-Type:text/html;Charset=utf-8');

$arrUsers = array(

    array('id'   => 1,'name' => '张三','age'  => 25,),

    array('id'   => 2,'name' => '李四','age'  => 23,),

    array('id'   => 3,'name' => '王五','age'  => 40,),

    array('id'   => 4,'name' => '赵六','age'  => 31,),

    array('id'   => 5,'name' => '黄七','age'  => 20,),

);

$arrSort = array();

foreach($arrUsers as $uniqid => $row){

    foreach($row as $key=>$value){

        $arrSort[$key][$uniqid] = $value;

    }

}

//$arrSort 为

// array(

//   "id"=>array(1,2,3,4,5),

//   "name"=>array("张三","李四","王五","赵六","黄七"),

//   "age"=>array(25,23,40,31,20)

// );

//array_multisort(排序字段，倒序/顺序，数组)

array_multisort($arrSort['age'], constant('SORT_DESC'), $arrUsers);

echo '<pre>';

var_dump($arrUsers);

/*

输出结果：

array(5) {

  [0]=>

  array(3) {

    ["id"]=>

    int(3)

    ["name"]=>

    string(6) "王五"

    ["age"]=>

    int(40)

  }

  [1]=>

  array(3) {

    ["id"]=>

    int(4)

    ["name"]=>

    string(6) "赵六"

    ["age"]=>

    int(31)

  }

  [2]=>

  array(3) {

    ["id"]=>

    int(1)

    ["name"]=>

    string(6) "张三"

    ["age"]=>

    int(25)

  }

  [3]=>

  array(3) {

    ["id"]=>

    int(2)

    ["name"]=>

    string(6) "李四"

    ["age"]=>

    int(23)

  }

  [4]=>

  array(3) {

    ["id"]=>

    int(5)

    ["name"]=>

    string(6) "黄七"

    ["age"]=>

    int(20)

  }

}

*/