在 Foreach 循环中调用回调函数时，如何避免静态变量导致的结果累积问题？

foreach ($towns as $key=>$val){
    $areaidarr = getchildareaid($val['id']);
    $result[$val['name']] = $worker::where('area_id','in',$areaidarr)->count();
}

function getChildAreaId($id){
    static $area;
    $area = $area ?? new \app\common\model\Area;
    $result = collection($area->where(['pid'=>$id])->order('id desc')->select())->toArray();
    static $res = []; // 问题所在：静态变量导致结果累积
    if($result){
        foreach ($result as $key=>$val) {
            $res[] = $val['id'];
            getChildAreaId($val['id']);
        }
    }
    return $res;
}

function getChildAreaId($id){
    $area = new \app\common\model\Area;
    $result = collection($area->where(['pid'=>$id])->order('id desc')->select())->toArray();
    $res = []; // 初始化一个新的空数组
    if($result){
        foreach ($result as $key=>$val) {
            $res[] = $val['id'];
            $res = array_merge($res, getChildAreaId($val['id'])); // 递归调用并合并结果
        }
    }
    return $res;
}

WITH RECURSIVE ChildAreas AS (
    SELECT id, pid FROM area WHERE pid = ?  --  替换 ? 为父级ID
    UNION ALL
    SELECT a.id, a.pid FROM area a
    INNER JOIN ChildAreas ca ON a.pid = ca.id
)
SELECT id FROM ChildAreas;