Use ST_PointN to return the Nth point of a LineString - PolarDB

Returns the Nth point of a LineString or circular LineString object.

Syntax

geometry ST_PointN(geometry aLinestring, integer n)

Parameter	Description
`aLinestring`	The LineString object or circular LineString object to query.
`n`	The index of the point to return. Negative values count backward from the end: `-1` returns the last point.

Returns NULL if aLinestring is not a LineString.
To get the Nth point of each LineString in a MultiLineString, combine ST_PointN with ST_Dump.
Supports circular strings and curves.
Supports 3D geometries and preserves Z coordinates.

Return the first point of a LineString:

SELECT ST_AsText(ST_PointN('LINESTRING(0 0,2 2)'::geometry, 1));

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

Return the last point using a negative index:

SELECT ST_AsText(ST_PointN('LINESTRING(0 0,2 2)'::geometry, -1));

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