按值分组并从点(纬度和经度)中为T-SQL中的每个组创建地理折线 [英] Group by value and create geography polyline from points (latitude and longitude) for each group in T-SQL

问题描述

有人在这里问过类似的问题:

A similar question has been asked here:

从T-SQL中的点创建地理折线

再提一个问题，我有一个如下所示的表模式:

Taking that question further, I have a table schema that looks like this:

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

样本数据如下:

如何使用TSQL将这些点转换为每个SensorID的地理折线 (这样我将为每个SensorID都有一个SensorID/折线记录)?

How can I convert these points into a geography polyline for each SensorID using TSQL (so that I would have a SensorID/Polyline record for each SensorID)?

我尝试使用db_cursor，但是每个组都有一个单独的结果集(我认为地理位置可能是相同的).这段代码:

I've tried using a db_cursor but I get a separate result set for each group (and I think the geographies might be the same). This code:

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:

最终，我想查看一个返回所有SensorID/折线对的视图.我不知道我当前的方法会奏效.我将不胜感激任何建议或示例.

Ultimately, I'd like to have a view returning all of the SensorID/Polyline pairs. I don't know that my current approach is going to work. I would appreciate any suggestions or examples.

推荐答案

在SQL Server 2017+中，您可以使用:

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

DBFiddle Demo

我尝试使用db_cursor，但是每个组都有一个单独的结果集

I've tried using a db_cursor but I get a separate result set for each group

请避免使用光标，每行以分号结尾并停止使用:

Please avoid cursors, end each line with semicolon and stop using:

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

上面的构造看起来不错，但是可能导致不确定的行为.更多信息: nvarchar串联/索引/nvarchar(max)莫名其妙的行为

Construct above may look ok, but it could lead to undefined behaviour. More info: nvarchar concatenation / index / nvarchar(max) inexplicable behavior

SQL Server 2012版本:

SQL Server 2012 version:

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

DBFiddle Demo2

要避免:

在执行用户定义的例程或聚合地理位置"期间发生.NET Framework错误:

A .NET Framework error occurred during execution of user-defined routine or aggregate "geography":

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.

System.FormatException: 24117: The LineString input is not valid because it does not have enough points. A LineString must have at least two points.

您可以添加HAVING COUNT(*) > 1;

最终

如果您有垃圾数据"，则将其过滤掉(或在该列上添加CHECK约束):

If you have "garbage data", just filter it out(or add CHECK constraint on that column):

纬度值必须在-90到90度之间"

"Latitude values must be between -90 and 90 degrees"

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 Demo3

DBFiddle Demo3

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