The CUME_DIST() function was first introduced with window
functions in MariaDB 10.2.0.
 
Syntax
------ 
CUME_DIST() OVER ( 
 [ PARTITION BY partition_expression ] 
 [ ORDER BY order_list ]
)
 
Description
----------- 
CUME_DIST() is a window function that returns the cumulative
distribution of a given row. The following formula is used
to calculate the value:
 
(number of rows 

URL: https://mariadb.com/kb/en/cume_dist/