Django对postgresql数据库进行分组聚合查询

action(methods=['GET'], detail=False, url_path='count')
def count(self, request):
    """统计最近30天的抓拍记录"""

    starttime = request.query_params.get('starttime')
    endtime = request.query_params.get('endtime')
    days = datetime.timedelta(days=1)

    start_date = datetime.datetime.strptime(starttime, '%Y%m%d%H%M%S').date()
    end_date = datetime.datetime.strptime(endtime, '%Y%m%d%H%M%S').date()

    count_list = {
        'dates': {
            'start_date': start_date,
            'end_date': end_date
        },
        'result': []
    }
    
    if end_date - start_date == days:
        result_list = models.DevicePhotoModel.objects.filter(take_photo_time__range=(start_date, end_date))
            .extra(select={"take_photo_time": "to_char(take_photo_time, 'HH')"}).values('take_photo_time') 
            .annotate(count=Count('take_photo_time')).values('take_photo_time', 'count')
        # 统计当天的数据
    else:
        result_list = models.DevicePhotoModel.objects.filter(take_photo_time__range=(start_date, end_date)) 
            .extra(select={"take_photo_time": "to_char(take_photo_time, 'yyyy-mm-dd')"}).values('take_photo_time') 
            .annotate(count=Count('take_photo_time')).values('take_photo_time', 'count')

    for result in result_list:
        count_list['result'].append({
            'date': result['take_photo_time'],
            'count': result['count']
        })

    return Response(count

mysql和postgres数据库格式化方法不同。网上找了很多格式化案例，但是都会报错。mysql中用DATE_FORMAT格式化，postgresql中用TO_CHAR格式化，格式化参数也有些许差别