usort($task, function($task_prev, $task_next) {
    if($task_prev['create_time'] != $task_next['create_time']){
        return ($task_prev['create_time'] > $task_next['create_time']) ? 1 : -1; //从小到大排序
        //return ($a_prev['year'] >  $a_next['year']) ? -1 : 1; //从大到小排序
    }
});


//或者
$a = [
    ['year'=>1992,'month'=>4,'num'=>3],
    ['year'=>1993,'month'=>1,'num'=>2],
    ['year'=>1992,'month'=>2,'num'=>1]
];
usort($a, function($a_prev, $a_next) {
            if($a_prev['year'] !=  $a_next['year']){
                return ($a_prev['year'] >  $a_next['year']) ? 1 : -1; //从小到大排序
                //return ($a_prev['year'] >  $a_next['year']) ? -1 : 1; //从大到小排序
            }else{
            if ($a_prev['month'] == $a_next['month']) return 0;
                return ($a_prev['month'] >  $a_next['month']) ? 1 : -1; //从小到大排序
              //return ($a_prev['month'] >  $a_next['month']) ? -1 : 1; //从大到小排序
            }
        });