ST_StartPoint-PolarDB(PolarDB)-阿里云帮助中心

Returns the start point of a LineString or circular LineString. Returns NULL for any other geometry type.

Syntax

geometry ST_StartPoint(geometry geomA)

Parameter	Description
`geomA`	The geometry object.

Preserves z coordinates — 3D geometries are supported and z values are not dropped.
Supports circular strings and curves, not just standard LineStrings.

SELECT ST_AsText(ST_StartPoint('LINESTRING(0 0,2 2)'::geometry));

Result:

 st_astext
------------
 POINT(0 0)
(1 row)

SELECT ST_StartPoint('POINT(0 1)'::geometry) IS NULL AS is_null;

Result:

 is_null
----------
 t
(1 row)

SELECT ST_AsEWKT(ST_StartPoint('LINESTRING(0 1 1, 0 2 2)'::geometry));

Result:

 st_asewkt
------------
 POINT(0 1 1)
(1 row)

SELECT ST_AsText(ST_StartPoint('CIRCULARSTRING(5 2,-3 1.999999, -2 1, -4 2, 6 3)'::geometry));

Result:

 st_astext
------------
 POINT(5 2)
(1 row)