以下是一个示例代码，演示了如何按照开始时间对已完成的请求进行排序：

requests = [
    {"id": 1, "start_time": "2022-01-01 10:00:00", "status": "completed"},
    {"id": 2, "start_time": "2022-01-02 09:00:00", "status": "completed"},
    {"id": 3, "start_time": "2022-01-03 14:00:00", "status": "completed"},
    {"id": 4, "start_time": "2022-01-01 15:00:00", "status": "completed"},
    {"id": 5, "start_time": "2022-01-02 11:00:00", "status": "completed"},
]

sorted_requests = sorted(requests, key=lambda req: req["start_time"])
for req in sorted_requests:
    print(f"Request ID: {req['id']}, Start Time: {req['start_time']}")

输出结果将按照开始时间升序排列：

Request ID: 1, Start Time: 2022-01-01 10:00:00
Request ID: 4, Start Time: 2022-01-01 15:00:00
Request ID: 2, Start Time: 2022-01-02 09:00:00
Request ID: 5, Start Time: 2022-01-02 11:00:00
Request ID: 3, Start Time: 2022-01-03 14:00:00

在示例代码中，我们使用了sorted()函数，其中的key参数指定了排序的关键字。通过lambda函数，我们将每个请求的开始时间作为排序的依据。最终，使用循环遍历排序后的请求列表，并打印每个请求的ID和开始时间。