【适用对象】
| Myslq | Mongodb | Elasticsearch
| --- | --- | --- |
| √ | √ | √ |
【使用说明】
返回查询指定字段的平均值得
【代码示例】
mysql
```
$avg=Db::name("zdh_card")->where("card_id>0")->avg("free_money");
```
mongodb
```
$avg=Db::mongo("zdh_card")->where(['card_id'=>arrayp[$gt'=>0])->avg("free_money");
```
Elasticsearch
```
$where=[];
$where=[
"range"=>["id"=>array('gt'=>2000)]
];
$resault=Db::elasticsearch("voideo")->where($where)->avg("id");
```
