回答

使用aggregate，结合group及max min sum，具体代码如下：

<?php
$manager = new MongoDB\Driver\Manager("mongodb://localhost:27017");

// 插入数据
$bulk = new MongoDB\Driver\BulkWrite;

$bulk->insert(['x' => 2, 'name' =>'bfw','scores'=>123]);
$bulk->insert(['x' => 2, 'name' =>'google','scores'=>10]);
$bulk->insert(['x' => 2, 'name' =>'baidu','scores'=>11]);
$bulk->insert(['x' => 2, 'name' =>'bfw','scores'=>200]);
$_data=$manager->executeBulkWrite('test.sites2', $bulk);


$param = [
    'aggregate' => 'sites2', //表名
    'pipeline'  => [
        ['$match' => ['x' => 2]],
        ['$group' => ['_id' => '$name', 'avg' => ['$avg' => '$scores'], 'count' => ['$sum' => 1]]],
    ],
    'cursor'    => new \stdClass()// 高版本需要带上这个值
];
//除了$sum外还有$max最大值 $min最小值 $avg平均值

$command = new \MongoDB\Driver\Command($param);
$cursor = $manager->executeCommand('test', $command);
foreach ($cursor as $document) {
    $document = objectToArray($document);
    var_dump($document);
}

function objectToArray($object){
    $result = array();
    $object = is_object($object) ? get_object_vars($object) : $object;
    foreach ($object as $key => $val) {
        $val = (is_object($val) || is_array($val)) ? objectToArray($val) : $val;
        $result[$key] = $val;
    }
    return $result;
}