按值分组并根据T-SQL

Question

这里也提出了类似的问题：

Create geography polyline from points in T-SQL

进一步提出这个问题，我有一个如下所示的表模式：

CREATE TABLE [dbo].[LongAndLats](
[Longitude] [float] NULL,
[Latitude] [float] NULL,
[SortOrder] [bigint] NULL,
[SensorID] [bigint] NULL,
)

示例数据如下所示：

如何使用TSQL将这些点转换为每个SensorID 的地理折线（以便我为每个SensorID设置SensorID / Polyline记录）？

我尝试过使用db_cursor，但我为每个组获得了一个单独的结果集（我认为这些地理位置可能是相同的）。这段代码：

DECLARE @SensorID VARCHAR(2000)
DECLARE @LineFromPoints geography
DECLARE @BuildString NVARCHAR(MAX)

DECLARE db_cursor CURSOR FOR  
SELECT Distinct([SensorId]) 
FROM [dbo].[LongAndLats]

OPEN db_cursor   
FETCH NEXT FROM db_cursor INTO LongAndLats 

WHILE @@FETCH_STATUS = 0   
BEGIN   
       SELECT @BuildString = COALESCE(@BuildString + ',', '') + CAST([Longitude] AS NVARCHAR(50)) + ' ' + CAST([Latitude] AS NVARCHAR(50))
       FROM [LongAndLats]
       WHERE SensorID = @SensorID
       ORDER BY SortOrder            

       SET @BuildString = 'LINESTRING(' + @BuildString + ')';   
       SET @LineFromPoints = geography::STLineFromText(@BuildString, 4326);
       SELECT @LineFromPoints As 'Geomerty', @name As 'SensorID' 

       FETCH NEXT FROM db_cursor INTO @name   
END   

CLOSE db_cursor   
DEALLOCATE db_cursor

结果如下：

最终，我想要一个返回所有SensorID / Polyline对的视图。我不知道我目前的做法是否有效。我将不胜感激任何建议或例子。

Answer 1

从SQL Server 2017+你可以使用：

SELECT geography::STLineFromText('LINESTRING(' + 
         STRING_AGG(CONCAT(Longitude, ' ' ,Latitude), ',') 
         WITHIN GROUP(ORDER BY SortOrder) + ')' , 4326) AS geometry
      ,SensorId
FROM dbo.LongAndLats
GROUP BY SensorId
HAVING COUNT(*) > 1;

<强> DBFiddle Demo

  

我尝试过使用db_cursor，但我为每个组获得了单独的结果集

请避免使用游标，以分号结束每一行并停止使用：

SELECT @BuildString = COALESCE(@BuildString + ',', '') 
       + CAST([Longitude] AS NVARCHAR(50)) + ' ' + CAST([Latitude] 
        AS NVARCHAR(50))
FROM [LongAndLats]
WHERE SensorID = @SensorID
ORDER BY SortOrder;  

上面的构造可能看起来不错，但它可能导致未定义的行为。更多信息：nvarchar concatenation / index / nvarchar(max) inexplicable behavior

修改

SQL Server 2012版：

SELECT geography::STLineFromText('LINESTRING(' 
      + STUFF(
             (SELECT ',' + CONCAT(Longitude, ' ' ,Latitude) 
              FROM dbo.LongAndLats t2
              WHERE t1.SensorId = t2.SensorId 
              ORDER BY SortOrder
              FOR XML PATH (''))
             , 1, 1, '')
       + ')' 
       , 4326) AS geometry, SensorId
FROM dbo.LongAndLats t1
GROUP BY SensorId
HAVING COUNT(*) > 1;

<强> DBFiddle Demo2

<强> EDIT2：

要避免：

  

在执行用户定义的例程或聚合＆＃34; geography＆＃34;：

期间发生.NET Framework错误      

System.FormatException：24117： LineString输入无效，因为它没有足够的点数。 LineString必须至少有两个点。

您可以添加HAVING COUNT(*) > 1;

最终编辑：

如果您有＆＃34;垃圾数据＆＃34;，只需将其过滤掉（或在该列上添加CHECK约束）：

  

＆＃34;纬度值必须介于-90和90度之间＆＃34;

SELECT geography::STLineFromText('LINESTRING(' 
      + STUFF(
             (SELECT ',' + CONCAT(Longitude, ' ' ,Latitude) 
              FROM dbo.LongAndLats t2
              WHERE t1.SensorId = t2.SensorId 
                AND Latitude BETWEEN -90 and 90
                AND Longitude BETWEEN -180 AND 180
              ORDER BY SortOrder
              FOR XML PATH (''))
             , 1, 1, '')
       + ')' 
       , 4326) AS geometry, SensorId
FROM dbo.LongAndLats t1
WHERE Latitude BETWEEN -90 and 90
  AND Longitude BETWEEN -180 AND 180
GROUP BY SensorId
HAVING COUNT(*) > 1;

<强> DBFiddle Demo3