描述

用给定点替换线字符串的第 N 个点。索引从 0 开始。负索引从后向前计数，因此 -1 是最后一个点。这在触发器中特别有用，当试图在某个顶点移动时维护连接点的关系。

可用性：1.1.0

更新 2.3.0：负索引

此函数支持 3d 并且不会丢弃 z 索引。

示例

--Change first point in line string from -1 3 to -1 1
SELECT ST_AsText(ST_SetPoint('LINESTRING(-1 2,-1 3)', 0, 'POINT(-1 1)'));
	   st_astext
-----------------------
 LINESTRING(-1 1,-1 3)

---Change last point in a line string (lets play with 3d linestring this time)
SELECT ST_AsEWKT(ST_SetPoint(foo.geom, ST_NumPoints(foo.geom) - 1, ST_GeomFromEWKT('POINT(-1 1 3)')))
FROM (SELECT ST_GeomFromEWKT('LINESTRING(-1 2 3,-1 3 4, 5 6 7)') As geom) As foo;
	   st_asewkt
-----------------------
LINESTRING(-1 2 3,-1 3 4,-1 1 3)

SELECT ST_AsText(ST_SetPoint(g, -3, p))
FROM ST_GEomFromText('LINESTRING(0 0, 1 1, 2 2, 3 3, 4 4)') AS g
	, ST_PointN(g,1) as p;
	   st_astext
-----------------------
LINESTRING(0 0,1 1,0 0,3 3,4 4)

			

另请参见

ST_AddPoint, ST_NPoints, ST_NumPoints, ST_PointN, ST_RemovePoint