编辑代码

<?php 
# 此代码无法直接运行，请先安装 mongodb 扩展以及 mongodb/mongodb 封装库

# 以下代码可在 PHP7.2、mongodb/mongodb ^1.0.0 环境下运行

// composer require mongodb/mongodb 
require('../vendor/autoload.php');

$client = new MongoDB\Client('mongodb://127.0.0.1:27017');

$collection = $client->selectCollection('study', 'test');

# 参考：https://docs.mongodb.com/manual/reference/operator/aggregation/sample/
$cursor = $collection->aggregate([
    [
        '$sample' => [
            'size' => 1
        ]
    ]
]);

foreach ($cursor as $document) {
    var_dump($document);
}