Returns the position of a value relative to all values in the partition.
The OVER clause of the window function must include an ORDER BY clause (Databricks SQL).
If the order is not unique the duplicates share the same relative later position.
cume_dist() over(order by expr) is similar, but not identical to
rank() over(order by position) / count(*) since rank ranking window function (Databricks SQL) produces the earliest absolute order.