ST_POINTN

Introduced or updated: v1.2.458

Returns a Point at a specified index in a LineString.

Syntax

ST_POINTN(<geometry>, <index>)

Arguments

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

备注

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

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)      │
└─────────────────┘