CUME_DIST

Calculates the cumulative distribution of each row's value. Returns the fraction of rows with values less than or equal to the current row's value.

See also: PERCENT_RANK

Syntax

CUME_DIST()
OVER (
    [ PARTITION BY partition_expression ]
    ORDER BY sort_expression [ ASC | DESC ]
)

Arguments:

• PARTITION BY: Optional. Divides rows into partitions
• ORDER BY: Required. Determines the distribution order
• ASC | DESC: Optional. Sort direction (default: ASC)

Notes:

• Returns values between 0 and 1 (exclusive of 0, inclusive of 1)
• Formula: (number of rows ≤ current value) / (total rows)
• Always returns 1.0 for the highest value(s)
• Useful for calculating percentiles and cumulative percentages

Examples

-- Create sample data
CREATE TABLE scores (
    student VARCHAR(20),
    score INT
);

INSERT INTO scores VALUES
    ('Alice', 95),
    ('Bob', 87),
    ('Charlie', 87),
    ('David', 82),
    ('Eve', 78);

Calculate cumulative distribution (showing what percentage of students scored at or below each score):

SELECT student, score,
       CUME_DIST() OVER (ORDER BY score) AS cume_dist,
       ROUND(CUME_DIST() OVER (ORDER BY score) * 100) AS cumulative_percent
FROM scores
ORDER BY score;

Result:

student | score | cume_dist | cumulative_percent
--------+-------+-----------+-------------------
Eve     |    78 |       0.2 |                20
David   |    82 |       0.4 |                40
Bob     |    87 |       0.8 |                80
Charlie |    87 |       0.8 |                80
Alice   |    95 |       1.0 |               100