Understanding MySQL 8.0 Window Functions: Concepts, Examples, and Use Cases

Window functions in MySQL 8.0 allow operations over a set of rows (a window) without collapsing the result set, enabling ranking, cumulative distribution, and other analytical calculations.

After a brief conceptual explanation, the article creates a sample user table and demonstrates the basic syntax:

SELECT createtime,
row_number() OVER (ORDER BY createtime) AS cr
FROM user ;

showing how row_number() assigns sequential numbers within the ordered window.

Several practical scenarios are presented:

Calculating each user's transaction amount as a percentage of total transactions using SUM(... ) OVER () and subqueries.

Identifying the top‑earning user for each day with ROW_NUMBER() OVER (PARTITION BY paydate ORDER BY total DESC) .

Both examples combine subqueries, window aggregates, and ordering to achieve the desired results.

The article then lists all window functions introduced in MySQL 8.0:

CUME_DIST()
DENSE_RANK()
FIRST_VALUE()
LAG()
LAST_VALUE()
LEAD()
NTH_VALUE()
NTILE()
PERCENT_RANK()
RANK()
ROW_NUMBER()

A detailed example of CUME_DIST() is provided, illustrating its output on a sample user1 table:

SELECT id,
CUME_DIST() OVER w AS ll,
createtime
FROM user1 WINDOW w AS (ORDER BY createtime);

Readers are directed to the official MySQL documentation for further details.