Vertex closer to another - Postgis

Question

Is it possible to return the nearest vertex to another? One of the observed geometries is a linestring. As in the figure below:

I want to return the single vertex of the linestring (which is represented by the black dots) which is closest to the red dot (which does not belong to the linestring, but is over it). Is there any function in postgis for that?

Answer 1

You can use the function: St_closestpoint()

SELECT 
    ST_AsText(ST_ClosestPoint(linha_qualquer, ponto_escolhido)) AS vertice_mais_proximo
FROM (
    SELECT
            l.geom AS linha_qualquer,
            p.geom AS ponto_escolhido
    FROM 
            linhas l, pontos p
    WHERE 
            p.gid = 1
) AS foo;