Cumulative distribution functions
Explore this snippet with some demo data here .
Description
Cumulative distribution functions (CDF) are a method for analysing the distribution of a quantity, similar to histograms. They show, for each value of a quantity, what fraction of rows are smaller or greater.
One method for calculating a CDF is as follows:
select
 Use a row_number window function to get the position of this row and CAST to convert row_number and count from integers to decimal
CAST(row_number() over (order by <quantity> asc) AS DECIMAL)/CAST((select count(*) from <table>) AS DECIMAL) AS cdf
from <table>
where

quantity
 the column containing the metric of interest 
table
 the table name
Note: CAST is used to convert the numerator and denominator of the fraction into decimals before they are divided.
Example
Using some student test scores as an example data source, let’s identify:

table
 this is calledExample_data

quantity
 this is thecolumn score
then the query becomes:
select
student_id,
score,
CAST(row_number() over (order by score asc) AS DECIMAL)/CAST((select count(*) from Example_data) AS DECIMAL) AS frac
from Example_data
student_id  score  frac 

3  76  0.2 
5  77  0.2 
4  82  0.6 
…  …  … 
1  97  1 