考试类型的表jx_exam_type，可后台添加内容

考试成绩的表jx_result，可后台添加内容

期中考试成绩表中的exam_id对应考试类型表中的id，也就是添加的成绩是属于期中还是期末

然后使用php查询

$sql="SELECT re.type, re.score, re.exam_id, et.title, DATE_FORMAT(et.addtime, '%Y-%m-%d') AS etime FROM jx_result AS re LEFT JOIN jx_exam_type AS et ON re.exam_id = et.id WHERE re.uid = '$uid' ORDER BY et.addtime DESC";

$result=$db->query($sql);

while($row=$result->fetch_assoc()){

$arr[]=$row;

}

echo json_encode($arr);

输出的格式如下

[

{

"type": "语文",

"score": "91",

"exam_id": "2",

"title": "三年级期末考试",

"etime": "2017-06-02"

},

{

"type": "英语",

"score": "89",

"exam_id": "2",

"title": "三年级期末考试",

"etime": "2017-06-02"

},

{

"type": "数学",

"score": "60",

"exam_id": "2",

"title": "三年级期末考试",

"etime": "2017-06-02"

},

{

"type": "数学",

"score": "91",

"exam_id": "1",

"title": "三年级期中考试",

"etime": "2017-05-25"

},

{

"type": "语文",

"score": "85",

"exam_id": "1",

"title": "三年级期中考试",

"etime": "2017-05-25"

},

{

"type": "英语",

"score": "87",

"exam_id": "1",

"title": "三年级期中考试",

"etime": "2017-05-25"

}

]

请问我如何才能将以上输出的json格式变为以下这种

{

"title": "三年级期中考试",

"etime": "2017-05-25",

"exam_id": [

{

"type": "数学",

"score": "91",

"exam_id": "1"

},

{

"type": "语文",

"score": "85",

"exam_id": "1"

},

{

"type": "英语",

"score": "87",

"exam_id": "1"

}

],

"title": "三年级期末考试",

"etime": "2017-06-02",

"exam_id": [

{

"type": "语文",

"score": "91",

"exam_id": "2"

},

{

"type": "英语",

"score": "89",

"exam_id": "2"

},

{

"type": "数学",

"score": "60",

"exam_id": "2"

}

]

}

变为以上这种格式后输出到前台，通过JS来输出到html上面

(可能我写的想要的格式有问题，不过大概意思就是将原来的数据根据exam_id来归类一下再输出)

目前正在学习中，很多地方不是很懂，求指教~~谢谢