フラスコレスレスで "group_by" SQLクエリを構築するには？

Question

私はflask_sqlalchemyとflask_restlessを使用して、PostgreSQLデータベースからデータにアクセスするAPIエンドポイントを作成しています。フラスコ不安定で次のSQLクエリを作成するにはどうすればよいですか？

SELECT AVG("SpeedBand"), "Location" 
FROM public.traffic_data 
WHERE "RoadName"='ABC ROAD' 
GROUP BY "Location" 

これは、すべての "ABC ROAD" を所属座標ペアと座標の各ペアの平均速度を返す：

avg | Location 
------------------------ 
1)'1.52' | 'X1 Y1 X2 Y2' 
2)'1.85' | 'X3 Y3 X4 Y4' 
------------------------ 

現在、このクエリ：

http://127.0.0.1:5000/api/traffic_data?q={"filters":[{"name":"RoadName","op":"==","val":"ABC ROAD"}]} 

戻り値を「ABC ROAD」に属するすべてのデータのJSON文字列と、異なる時刻のすべての速度データ：

{ 
    "num_results": 26, 
    "objects": [ 
    { 
     "DateTime": "2017-09-07T19:25:37.035325", 
     "LinkID": "109002906", 
     "Location": "X1 Y1 X2 Y2", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 3, 
     "id": 34094 
    }, 
    { 
     "DateTime": "2017-09-07T19:25:37.035325", 
     "LinkID": "109002907", 
     "Location": "X3 Y3 X4 Y4", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 1, 
     "id": 38003 
    }, 
    { 
     "DateTime": "2017-09-13T09:57:07.163900", 
     "LinkID": "109002906", 
     "Location": "X1 Y1 X2 Y2", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 1, 
     "id": 92874 
    }, 
    { 
     "DateTime": "2017-09-13T09:57:07.163900", 
     "LinkID": "109002907", 
     "Location": "X3 Y3 X4 Y4", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 1, 
     "id": 96783 
    }, 
    { 
     "DateTime": "2017-09-13T09:57:07.163900", 
     "LinkID": "109002906", 
     "Location": "X1 Y1 X2 Y2", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 1, 
     "id": 114755 
    }, 
    { 
     "DateTime": "2017-09-13T09:57:07.163900", 
     "LinkID": "109002907", 
     "Location": "X3 Y3 X4 Y4", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 2, 
     "id": 114756 
    }, 
    { 
     "DateTime": "2017-09-13T10:08:17.727949", 
     "LinkID": "109002906", 
     "Location": "X1 Y1 X2 Y2", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 2, 
     "id": 151654 
    }, 
    { 
     "DateTime": "2017-09-13T10:08:17.727949", 
     "LinkID": "109002907", 
     "Location": "X3 Y3 X4 Y4", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 2, 
     "id": 155563 
    }, 
    { 
     "DateTime": "2017-09-13T10:19:39.040191", 
     "LinkID": "109002906", 
     "Location": "X1 Y1 X2 Y2", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 2, 
     "id": 210434 
    }, 
    { 
     "DateTime": "2017-09-13T10:19:39.040191", 
     "LinkID": "109002907", 
     "Location": "X3 Y3 X4 Y4", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 2, 
     "id": 214343 
    }, 
    { 
     "DateTime": "2017-09-13T10:27:51.307349", 
     "LinkID": "109002906", 
     "Location": "X1 Y1 X2 Y2", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 2, 
     "id": 269214 
    }, 
    { 
     "DateTime": "2017-09-13T10:42:36.724985", 
     "LinkID": "109002906", 
     "Location": "X1 Y1 X2 Y2", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 2, 
     "id": 327994 
    }, 
    { 
     "DateTime": "2017-09-13T10:42:36.724985", 
     "LinkID": "109002907", 
     "Location": "X3 Y3 X4 Y4", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 2, 
     "id": 331903 
    }, 
    { 
     "DateTime": "2017-09-13T10:42:36.724985", 
     "LinkID": "109002906", 
     "Location": "X1 Y1 X2 Y2", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 1, 
     "id": 349875 
    }, 
    { 
     "DateTime": "2017-09-13T10:42:36.724985", 
     "LinkID": "109002907", 
     "Location": "X3 Y3 X4 Y4", 
     "RoadName": "ABC ROAD", 
     "SpeedBand": 2, 
     "id": 349876 
    }, 

    . . . 


    ], 
    "page": 1, 
    "total_pages": 1 
} 

Answer 1

グループの場合、次の形式でフィールドを指定する必要があります。 GROUP_BY形態のオブジェクトのリスト：

{"field": <fieldname>} 

ここフィールド名によってグループによって使用されるカラムです。