ST_POINTN

Introduced or updated: v1.2.458

Returns a Point at a specified index in a LineString.

Syntax

ST_POINTN(<geometry_or_geography>, <index>)

Arguments

Arguments	Description
<geometry_or_geography>	The argument must be an expression of type GEOMETRY or GEOGRAPHY that represents a LineString.
<index>	The index of the Point to return.

note

The index is 1-based, and a negative index is uesed as the offset from the end of LineString. If index is out of bounds, the function returns an error.

Return Type

Geometry.

Examples

GEOMETRY examples

SELECT
  ST_POINTN(
    ST_GEOMETRYFROMWKT(
      'LINESTRING(1 1, 2 2, 3 3, 4 4)'
    ),
    1
  ) AS pipeline_pointn;

┌─────────────────┐
│ pipeline_pointn │
├─────────────────┤
│ POINT(1 1)      │
└─────────────────┘

SELECT
  ST_POINTN(
    ST_GEOMETRYFROMWKT(
      'LINESTRING(1 1, 2 2, 3 3, 4 4)'
    ),
    -2
  ) AS pipeline_pointn;

┌─────────────────┐
│ pipeline_pointn │
├─────────────────┤
│ POINT(3 3)      │
└─────────────────┘

GEOGRAPHY examples

SELECT
  ST_POINTN(
    ST_GEOGFROMWKT(
      'LINESTRING(1 1, 2 2, 3 3, 4 4)'
    ),
    2
  ) AS pipeline_pointn;

┌─────────────────┐
│ pipeline_pointn │
├─────────────────┤
│ POINT(2 2)      │
└─────────────────┘