mongodb aggregate group 分组我想要查询出来多个字段，该怎么写，例子里面都是只有_id跟另外一个聚合结果。
在initial中把你想要的字段标记出来,使用count,count_1,count_2,count_3来代表你要查询的字段。
query = {key:"value"}
initial = {
"count" : 0,
"count_1":0,
"count_2":0,
"count_3":0
}
reduce = function(doc,prev){
prev.count += doc.count;
prev.count_1 += doc.count_1;
prev.count_2 += doc.count_2;
prev.count_3 += doc.count_3;
}
db.test.group({
"key" : query,
"initial" :initial,
"$reduce" : reduce
})