基于array_multisort()函数

//测试数据
$data = [
    [
        "stu_id"=> 1,
        "number"=> "20171114000001",
        "join_at"=> "2017-11-14 12:36:16"
    ],
    [
        "stu_id"=> 2,
        "number"=> "20171114000002",
        "join_at"=> "2017-11-14 12:36:16"
    ],
    [
        "stu_id"=> 3,
        "number"=> "20171114000003",
        "join_at"=> "2017-11-14 13:36:14"
    ],
    [
        "stu_id"=> 4,
        "number"=> "20171114000004",
        "join_at"=> "2017-11-14 14:26:15"
    ],
];

//排序
foreach ($data as $key => $value) {
    //将需要排序的值提取出来作为一个数组
    $join_at[$key] = $value['join_at'];
    $number[$key] = $value['number'];
}

//根据join_at降序，number升序排序
array_multisort($join_at, SORT_DESC, $number, SORT_ASC, $data);
echo $data;

//排序结果
[
    {
        "stu_id": 4,
        "number": "20171114000004",
        "join_at": "2017-11-14 14:26:15"
    },
    {
        "stu_id": 3,
        "number": "20171114000003",
        "join_at": "2017-11-14 13:36:14"
    },
    {
        "stu_id": 1,
        "number": "20171114000001",
        "join_at": "2017-11-14 12:36:16"
    },
    {
        "stu_id": 2,
        "number": "20171114000002",
        "join_at": "2017-11-14 12:36:16"
    }
]