按值分组并根据T-SQL中每个组的点(纬度和经度)创建地理折线

Question

这里也提出了类似的问题:

从T-SQL中的点创建地理折线

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:

最后,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;

DBFiddle演示

我尝试过使用db_cursor但是我为每个组获得了一个单独的结果集

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)莫名其妙的行为

编辑:

SQL Server 2012版本:

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;

DBFiddle Demo2

EDIT2:

避免:

执行用户定义的例程或聚合"地理"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.LineString必须至少有两个点.

你可以添加HAVING COUNT(*) > 1;

最终编辑:

如果您有"垃圾数据",只需将其过滤掉(或CHECK在该列上添加约束):

"纬度值必须介于-90到90度之间"

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;

DBFiddle演示3