在elasticsearch中，我有一个数据表，其中有字段customer_id和event_date，我想按每个月计数，但不是所有数据，我想过滤掉重复的customer_id，除了第一条记录（具有最小事件日期）之前应用日期历史记录，请帮助我过滤查询。
这是我的样本数据：

"hits": [
            {
                "_index": "log_report",
                "_id": "5",
                "_score": 1.0,
                "_source": {
                    "created_at": "2021-08-23T02:36:10+00:00",
                    "created_by": -1,
                    "updated_at": "2021-08-23T02:36:10+00:00",
                    "updated_by": -1,
                    "is_deleted": false,
                    "account_id": 509,
                    "customer_id": 1961105,
                    "opened_at": "2021-08-23T02:36:10+00:00",
                    "id": 5
                }
            },
            {
                "_index": "log_report",
                "_id": "11",
                "_score": 1.0,
                "_source": {
                    "created_at": "2021-08-23T02:37:26+00:00",
                    "created_by": -1,
                    "updated_at": "2021-08-23T02:37:26+00:00",
                    "updated_by": -1,
                    "is_deleted": false,
                    "account_id": 509,
                    "customer_id": 1961105,
                    "opened_at": "2021-08-23T02:37:26+00:00",
                    "id": 11
                }
            },
            ...
       ]

我有字段customer_id和created_at，customer_id值可以在多个记录中具有相同值，但我只想处理每个customer_id第一个记录