ST_PointN method

Returns the nth point in the linestring.

Note

By default, ST_PointN uses the original format for a geometry, if it is available. Otherwise, the internal format is used. For more information about internal and original formats, see STORAGE FORMAT clause, CREATE SPATIAL REFERENCE SYSTEM statement.

Syntax

linestring-expression.ST_PointN(n)

Parameters

Name	Type	Description
n	INT	The position of the element to return, from 1 to linestring-expression.ST_NumPoints().

Returns

ST_Point If the value of linestring-expression is the empty set, returns NULL. If the specified position n is less than 1 or greater than the number of points, returns NULL. Otherwise, returns the ST_Point value at position n.
The spatial reference system identifier of the result is the same as the spatial reference system of the linestring-expression.

Standards and compatibility

Example

The following example returns the result Point (0 4).

SELECT TREAT( Shape AS ST_LineString ).ST_PointN( 2 )
FROM SpatialShapes WHERE ShapeID = 5

The following example returns one row for each point in geom.

BEGIN
    DECLARE geom ST_LineString;
    SET geom = NEW ST_LineString( 'LineString( 0 0, 1 0 )' );
    SELECT row_num, geom.ST_PointN( row_num )
        FROM sa_rowgenerator( 1, geom.ST_NumPoints() )
        ORDER BY row_num;
END

The example returns the following result set:

row_num	geom.ST_PointN(row_num)
`1`	`Point (0 0)`
`2`	`Point (1 0)`

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