thinkphp中想把数据库中取出的数据 和利用count统计出的数字合并到一个数组中

 Array
(
    [0] => Array
        (
            [paper_id] => 2
            [student] => 小丸子
            [subject] => 信息技术
            [sj_title] => 信息考试
            [paper_createtime] => 2015-10-14 13:39:08
        )

    [1] => Array
        (
            [paper_id] => 2
            [student] => 小丸子
            [subject] => 信息技术
            [sj_title] => 信息考试
            [paper_createtime] => 2015-10-14 13:39:08
        )

)

数组b

Array
(
    [0] => Array
        (
            [num] => 2
        )
     [2] => Array
        (
            [num] => 1
        )
)


    想要的结果：
     Array
(
    [0] => Array
        (
            [paper_id] => 2
            [student] => 小丸子
            [subject] => 信息技术
            [sj_title] => 信息考试
            [paper_createtime] => 2015-10-14 13:39:08
                        [num] => 2
        )

    [1] => Array
        (
            [paper_id] => 2
            [student] => 小丸子
            [subject] => 信息技术
            [sj_title] => 信息考试
            [paper_createtime] => 2015-10-14 13:39:08
                        [num] => 1
        )

)

试了数组合并array_merge_recursive 和array_merge貌似都不行，应该如何实现？

foreach($a as $key=>$val)
{
$a[$key]['num']=$b[$key]['num'];
}

array_push可以试试