按值分组并从 T-SQL 中的每个组的点（纬度和经度）创建地理折线

Question

这里有人问过类似的问题：

Create geography polyline from points in T-SQL

进一步研究这个问题，我有一个 table 架构，如下所示：

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 （以便每个 SensorID 都有一个 SensorID/Polyline 记录）？

我试过使用 db_cursor，但我得到了每个组的单独结果集（我认为地理位置可能相同）。此代码：

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：

最终，我想要一个返回所有 SensorID/Polyline 对的视图。我不知道我目前的方法是否有效。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 Demo

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

请避免游标，每行以分号结束并停止使用：

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没问题，但它可能会导致未定义的行为。更多信息：nvarchar concatenation / index / nvarchar(max) inexplicable behavior

编辑：

SQL服务器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

编辑2：

避免：

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

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

你可以添加 HAVING COUNT(*) > 1;

最终编辑：

如果您有 "garbage data"，只需将其过滤掉（或对该列添加 CHECK 约束）：

"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

按值分组并从 T-SQL 中的每个组的点（纬度和经度）创建地理折线

Group by value and create geography polyline from points (latitude and longitude) for each group in T-SQL

tsql

sql-server

geospatial

sqlgeography

sqlgeometry