cume_dist analytic window function
Applies to: 
Databricks SQL Databricks Runtime
Returns the position of a value relative to all values in the partition.
Syntax
cume_dist() over_clause
Arguments
- over_clause: The clause describing the windowing. See: Window functions.
Returns
A DOUBLE.
The OVER clause of the window function must include an ORDER BY clause.
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 produces the earliest absolute order.
Examples
> SELECT a, b, cume_dist() OVER (PARTITION BY a ORDER BY b)
FROM VALUES ('A1', 2), ('A1', 1), ('A2', 3), ('A1', 1) tab(a, b);
A1 1 0.6666666666666666
A1 1 0.6666666666666666
A1 2 1.0
A2 3 1.0