Name
ST_SetPoint — 用给定点替换线串的点。
Synopsis
geometry ST_SetPoint(geometry linestring, integer zerobasedposition, geometry point);
描述
将线串的 N 点替换为给定点。 索引从 0 开始。负索引向后计数，因此 -1 是最后一个点。当一个顶点移动时试图维持关节关系时，这在触发器中特别有用。
可用性：1.1.0
更新 2.3.0：负索引
该函数支持 3d 并且不会丢失 z-index。
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)