Question

我需要从有两个主键macid和deviceid的表中选择数据。

我需要记录集来按这两个主键对记录进行分组，但我无法弄清楚如何操作。

这就是我现在所拥有的：

SELECT * FROM data WHERE stamp > 1373040000000 AND stamp < 1373126400000 ORDER BY macid ASC,deviceid ASC,stamp ASC

[
{"deviceid":1,"temp":-19.81,"macid":"19:5d:ee3e00","stamp":1373054400000},
{"deviceid":1,"temp":-20.31,"macid":"19:5d:ee3e00","stamp":1373065200000},
{"deviceid":3,"temp":28.87,"macid":"19:5d:ee3e00","stamp":1373054400000},
{"deviceid":3,"temp":28.87,"macid":"19:5d:ee3e00","stamp":1373065200000}
]

这就是我需要的

[
[{"deviceid":1,"temp":-19.81,"macid":"19:5d:ee3e00","stamp":1373054400000},
{"deviceid":1,"temp":-20.31,"macid":"19:5d:ee3e00","stamp":1373065200000}]

[{"deviceid":3,"temp":28.87,"macid":"19:5d:ee3e00","stamp":1373054400000},
{"deviceid":3,"temp":28.87,"macid":"19:5d:ee3e00","stamp":1373065200000}]
]

我试过这个，但它只返回与第一个结果相同的内容：

SELECT * FROM data WHERE stamp > 1373040000000 AND stamp < 1373126400000 GROUP BY macid, deviceid, stamp ORDER BY macid ASC,deviceid ASC,stamp ASC

这可能吗？

Answer 1

实际上，您无法使SQL服务器返回多组行。 GROUP BY 语句用于按行对行进行分组，并计算其他列的聚合函数（行数，总和，平均值等）。结果，每个组只返回一行。

所以，我认为我们需要在客户端进行分组。你可以这样做：

var devices=[
{"deviceid":1,"temp":-19.81,"macid":"19:5d:ee3e00","stamp":1373054400000},
{"deviceid":1,"temp":-20.31,"macid":"19:5d:ee3e00","stamp":1373065200000},
{"deviceid":3,"temp":28.87,"macid":"19:5d:ee3e00","stamp":1373054400000},
{"deviceid":3,"temp":28.87,"macid":"19:5d:ee3e00","stamp":1373065200000}
];

var devicesGrouped = {};
for (i=0; i < devices.length; i++) 
{
   key = [devices[i].deviceid, devices[i].macid];
   if (!(key in devicesGrouped))
      devicesGrouped[key] = [];

   devicesGrouped[key].push(devices[i]);
}

结果将devicesGrouped哈希与[deviceid,macid]用作密钥：

{"1,19:5d:ee3e00":
     [{"deviceid":1,"temp":-19.81,"macid":"19:5d:ee3e00","stamp":1373054400000},
      {"deviceid":1,"temp":-20.31,"macid":"19:5d:ee3e00","stamp":1373065200000}],

 "3,19:5d:ee3e00":
     [{"deviceid":3,"temp":28.87,"macid":"19:5d:ee3e00","stamp":1373054400000},
      {"deviceid":3,"temp":28.87,"macid":"19:5d:ee3e00","stamp":1373065200000}]
}

SQL查询返回按主键分组

1 个答案: