Function ST_PointN 

pub fn ST_PointN<ls, n>(
    ls: ls,
    n: n,
) -> ST_PointN<<ls as AsExpression<LineString>>::Expression, <n as AsExpression<Integer>>::Expression>
where
    ls: AsExpression<LineString>,
    n: AsExpression<Integer>,

Represents the MySQL ST_PointN function