Categories:

Geospatial Functions

ST_POINTN

Returns a Point at a specified index in a LineString.

See also:

ST_ENDPOINT , ST_STARTPOINT

Syntax

ST_POINTN( <geography_or_geometry_expression> , <index> )

Arguments

geography_or_geometry_expression

The argument must be an expression of type GEOGRAPHY or GEOMETRY that represents a LineString.

index

The index of the Point to return. The index must be an integer.

A negative index is interpreted as the offset from the end of the LineString. For example, -1 is interpreted as the last Point in the LineString, -2 is interpreted as the second to the last Point, etc.

Returns

The function returns a value of type GEOGRAPHY or GEOMETRY that contains the Point at the specified index of the LineString.

Usage Notes

  • If geography_or_geometry_expression is not a LineString, the function reports an error.

  • If index is out of bounds (e.g. exceeds the number of Points in the LineString), the function reports an error.

Examples

GEOGRAPHY Examples

The following query returns the second Point in a LineString:

ALTER SESSION SET GEOGRAPHY_OUTPUT_FORMAT='WKT';
SELECT ST_POINTN(TO_GEOGRAPHY('LINESTRING(1 1, 2 2, 3 3, 4 4)'), 2);

+--------------------------------------------------------------+
| ST_POINTN(TO_GEOGRAPHY('LINESTRING(1 1, 2 2, 3 3, 4 4)'), 2) |
|--------------------------------------------------------------|
| POINT(2 2)                                                   |
+--------------------------------------------------------------+

The following query uses a negative index to return the second Point from the end of a LineString:

ALTER SESSION SET GEOGRAPHY_OUTPUT_FORMAT='WKT';
SELECT ST_POINTN(TO_GEOGRAPHY('LINESTRING(1 1, 2 2, 3 3, 4 4)'), -2);

+---------------------------------------------------------------+
| ST_POINTN(TO_GEOGRAPHY('LINESTRING(1 1, 2 2, 3 3, 4 4)'), -2) |
|---------------------------------------------------------------|
| POINT(3 3)                                                    |
+---------------------------------------------------------------+

GEOMETRY Examples

The following query returns the second Point in a LineString:

ALTER SESSION SET GEOMETRY_OUTPUT_FORMAT='WKT';
SELECT ST_POINTN(TO_GEOMETRY('LINESTRING(1 1, 2 2, 3 3, 4 4)'), 2);

+-------------------------------------------------------------+
| ST_POINTN(TO_GEOMETRY('LINESTRING(1 1, 2 2, 3 3, 4 4)'), 2) |
|-------------------------------------------------------------|
| POINT(2 2)                                                  |
+-------------------------------------------------------------+

The following query uses a negative index to return the second Point from the end of a LineString:

ALTER SESSION SET GEOMETRY_OUTPUT_FORMAT='WKT';
SELECT ST_POINTN(TO_GEOMETRY('LINESTRING(1 1, 2 2, 3 3, 4 4)'), -2);

+--------------------------------------------------------------+
| ST_POINTN(TO_GEOMETRY('LINESTRING(1 1, 2 2, 3 3, 4 4)'), -2) |
|--------------------------------------------------------------|
| POINT(3 3)                                                   |
+--------------------------------------------------------------+
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