Question

我通过连接wkt并将GEOMETRYCOLLECTION与STUFF结合使用，来强制ORDER BY中包含几何图形的顺序

（我正在使用SQL Server 2016，否则我将使用STRING_AGG）

DECLARE @OrderedGeometryList TABLE  
(  
    [GroupId] INT,
    [Geometry] GEOMETRY,
    [Order] INT
)  


INSERT @OrderedGeometryList
VALUES 
     (1, 'LINESTRING(3 3, 4 4)', 3)
    ,(1, 'LINESTRING(0 0, 1 1)', 1)
    ,(1, 'LINESTRING(1 1, 2 2)', 2)
    ,(2, 'POINT(35453 141)', 2)
    ,(2, 'MULTILINESTRING((0 0, 1 1),(2 2, 3 3))', 1)

然后

;WITH Grouped AS (
    SELECT 
        [GroupId]
        ,Geometry::STGeomCollFromText(
            'GEOMETRYCOLLECTION(' + 
                STUFF((
                    SELECT ',' + [Geometry].ToString()
                    FROM @OrderedGeometryList t2
                    WHERE t1.[GroupId] = t2.[GroupId] 
                    ORDER BY [Order]
                    FOR XML PATH ('')
                ), 1, 1, '')
            + ')', MAX([Geometry].STSrid)
        ) as [Geometry]
    FROM @OrderedGeometryList t1
    GROUP BY [GroupId]
)


SELECT GroupId, Geometry.ToString() as WKT
FROM Grouped

产生：

GroupId WKT
1   GEOMETRYCOLLECTION (LINESTRING (0 0, 1 1), LINESTRING (1 1, 2 2), LINESTRING (3 3, 4 4))
2   GEOMETRYCOLLECTION (MULTILINESTRING ((0 0, 1 1), (2 2, 3 3)), POINT (35453 141))

请注意收集顺序（从左到右）如何遵循表中指定的顺序。这是我所追求的效果，但是我很好奇是否有更干净的方法可以做到这一点。

我考虑编写自己的CLR聚合，然后将OVER()与ORDER BY一起使用，但似乎Is it possible to use user defined aggregates (clr) with window functions (over)?不支持此操作

Answer 1

您可以在子查询中使用OFFSET对行进行排序。

SELECT Geometry::CollectionAggregate([Geometry]).ToString() 
FROM 
    (SELECT * FROM @OrderedGeometryList ORDER BY [GroupId], [Order] OFFSET 0 ROWS) T
GROUP BY [GroupId]

结果：

GEOMETRYCOLLECTION (LINESTRING (0 0, 1 1), LINESTRING (1 1, 2 2), LINESTRING (3 3, 4 4))
GEOMETRYCOLLECTION (MULTILINESTRING ((0 0, 1 1), (2 2, 3 3)), POINT (35453 141))

指定CollectionAggregate使用的顺序

1 个答案: