public function update(Request $request, $id)
{
    //查询数据
    $student = Student::find($id);
    //判断请求
    if($request->isMethod('POST'))
    {
        $data = $request->input('Student');
        $student->name = $data['name'];
        $student->age = $data['age'];
        $student->sex = $data['sex'];

        if($student->save()){
            return redirect('student/index')->with('success','修改成功-'.$id);
        }
    }

    return view('student.update',[
        'student'=>$student
    ]);
}