mongodb php获取字段唯一值

<?php
// 连接MongoDB数据库
$mongoClient = new MongoDB\Client("mongodb://localhost:27017");

// 选择数据库和集合
$database = $mongoClient->selectDatabase("mydb");
$collection = $database->selectCollection("mycollection");

// 使用聚合管道操作获取字段的唯一值
$pipeline = [
    ['$group' => ['_id' => '$field_name']],
    ['$project' => ['_id' => 0, 'unique_values' => '$_id']]
];

$result = $collection->aggregate($pipeline);

// 输出唯一值
foreach ($result as $document) {
    echo $document['unique_values'] . "\n";
}
?>