CUME_DIST window function - Amazon Redshift

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 doesn't 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

Examples

The following example calculates the cumulative distribution of the quantity for each seller:

select sellerid, qty, cume_dist() over (partition by sellerid order by qty) from winsales; sellerid qty cume_dist -------------------------------------------------- 1 10.00 0.33 1 10.64 0.67 1 30.37 1 3 10.04 0.25 3 15.15 0.5 3 20.75 0.75 3 30.55 1 2 20.09 0.5 2 20.12 1 4 10.12 0.5 4 40.23 1

For a description of the WINSALES table, see Overview example for window functions.