SQL version of pointToTileFraction from https://github.com/mapbox/tilebelt/blob/master/index.js#L155

pointToTileFraction.sql

create or replace function pointToTileFraction(float, float, integer) returns int[3] as $$

declare 
    lon ALIAS FOR $1;
    lat ALIAS FOR $2;
    z ALIAS FOR $3;
    result int[];
BEGIN    
    result  := array_append(result, floor(pow(2,z) * (lon / 360 + 0.5))::int);
    result  := array_append(result, floor(pow(2,z) * (0.5-0.25 *(log((1 + sin(lat*pi()/180))/(1 - sin(lat*pi()/180)))/pi())))::int);
    result  := array_append(result, z);
    return result;
END;

$$ LANGUAGE 'plpgsql';