SQL:多边形的联合 [英] SQL: Union of polygons
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问题描述
我有一个包含多边形的单一列几何
类型的表。
I have a table with a single column of geometry
type, containing polygons. How do I get the union of all the polygons in the table?
推荐答案
这对我有效:
CREATE TABLE #g (i INT IDENTITY, a geometry)
INSERT INTO #g (a)
VALUES
(geometry::STGeomFromText(
'POLYGON((0 0, 3 0, 3 3, 0 3, 0 0))', 0)
),
(geometry::STGeomFromText(
'POLYGON((5 2, 7 2, 7 0, 5 0, 5 2))', 0)
)
DECLARE @g geometry
SELECT TOP 1 @g = a FROM [#g]
SELECT @g = @g.STUnion(a) FROM #g
SELECT @g
显然,当被调用的实例或操作数为空时,STUnion方法返回null,因此选择top 1
hack。
So, apparently, the STUnion method returns null when either the instance on which it's being called or the operand is null, hence the select top 1
hack.
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