Function ntile 

pub fn ntile<'a, V>(
    n: usize,
) -> WindowFnExpr<'a, V, <V::DialectMarker as CountPolicy>::Count, NonNull>
where
    V: SQLParam + 'a,
    V::DialectMarker: CountPolicy,

NTILE(n) — divide rows into n roughly equal groups.

Returns an integer, never NULL.