CUME_DIST window function
Calculates the cumulative distribution of a value within a window or partition. Assuming ascending ordering, the cumulative distribution is determined using this formula:
count of rows with values <= x / count of rows in the window or
partition
where x equals the value in the current row of the column specified in the ORDER BY clause. The following dataset illustrates use of this formula:
Row# Value Calculation CUME_DIST 1 2500 (1)/(5) 0.2 2 2600 (2)/(5) 0.4 3 2800 (3)/(5) 0.6 4 2900 (4)/(5) 0.8 5 3100 (5)/(5) 1.0
The return value range is >0 to 1, inclusive.
Syntax
CUME_DIST () OVER ( [ PARTITION BY partition_expression ] [ ORDER BY order_list ] )
Arguments
 OVER

A clause that specifies the window partitioning. The OVER clause cannot contain a window frame specification.
 PARTITION BY partition_expression

Optional. An expression that sets the range of records for each group in the OVER clause.
 ORDER BY order_list

The expression on which to calculate cumulative distribution. The expression must have either a numeric data type or be implicitly convertible to one. If ORDER BY is omitted, the return value is 1 for all rows.
If ORDER BY does not produce a unique ordering, the order of the rows is nondeterministic. For more information, see Unique ordering of data for window functions.
Return type
FLOAT8
Example
See CUME_DIST window function examples.