ST_PointN

Signature

POINT ST_PointN(GEOMETRY geometry, INT n);

Returns the nth point of geom if geom is a LINESTRING or a MULTILINESTRING containing exactly one LINESTRING; NULL otherwise.

Tip

Do I start counting from 0 or 1? → The index runs from 1 to n

Note

Implements the OpenGIS Simple Features Implementation Specification for SQL version 1.2.1

SELECT ST_PointN('LINESTRING(1 1, 1 6, 2 2, -1 2))', 2);
-- Answer: POINT(1 6)

SELECT ST_PointN('MULTILINESTRING((1 1, 1 6, 2 2, -1 2))', 3);
-- Answer: POINT(2 2)

SELECT ST_PointN('MULTIPOINT(1 1, 1 6, 2 2, -1 2)', 3);
-- Answer: NULL

This MULTILINESTRING contains two LINESTRINGs

SELECT ST_PointN('MULTILINESTRING((1 1, 1 6, 2 2, -1 2),
                                  (0 1, 2 4))', 3);
-- Answer: NULL

SELECT ST_PointN('LINESTRING(1 1, 1 6, 2 2, -1 2))', 0);
-- Answer: Point index out of range. Must be between 1 and ST_NumPoints.