小程序云函数中用group分组查询，只能查询20条，怎么解决？

用滚动条每次加10加载，希望对您有帮助。

fetchNickYMCount: function() {

db.collection('findingList').aggregate()

.group({

_id: {

userName: '$userName',

writeYM: '$writeYM',

},

t: $.sum(1)

})

.sort({

_id:-1

})

.skip(this.data.s)

.limit(this.data.l)

.end()



.then(res => {

this.setData({

result: this.data.result.concat(res.list)

})

// console.log(this.data.result)

})

},



lower:function(){

this.setData({

s:this.data.s+10,

l:this.data.l+10

})

this.fetchNickYMCount()

},

WXML:

<scroll-view scroll-y="true" class="scoll-h" lower-threshold="100"  bindscrolltolower="lower" style='height:878rpx;overflow-y: scroll;padding-top:1rpx;' >

<view class='history-table-wrap'>

<view class="table">

<view class="tr">

<view class="th th1">填写人</view>

<view class="th th2">填写年月</view>

<view class="th th3">共计</view>

</view>

<view class="tr" wx:for="{{result}}"  wx:key="{{index}}">

<view class="td td1">{{item._id.userName}}</view>

<view class="td td2">{{item._id.writeYM}}</view>

<view class="td td3">{{item.t}}</view>

</view>

</view>

</view>

</scroll-view>