How to Use Window Functions in MySQL

Galaxy Glossary

How do I use window functions in MySQL for analytics?

MySQL window functions perform calculations across sets of rows related to the current row without collapsing them.

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Description

Example H2

Example H3

Why choose window functions over GROUP BY?

Window functions keep each row visible while adding aggregates. This lets you compare row-level data with group totals, running totals, or rankings without extra self-joins.

When should I apply PARTITION BY?

Use PARTITION BY to restart the calculation for each logical group—customers, orders, or dates—while still scanning the whole result set in a single query.

How do ORDER BY and frame clauses work?

ORDER BY defines the sequence inside each partition.The frame clause (RANGE or ROWS) narrows which rows participate in the calculation, enabling running totals, moving averages, and period comparisons.

Best practice: alias calculated columns

Give every window calculation a clear alias—e.g., cumulative_total—to simplify downstream filtering, sorting, and client-side reading.

Best practice: filter with outer queries

Apply WHERE on an outer SELECT when filtering by a window alias. MySQL cannot reference the alias in the same SELECT level.

Can I combine multiple window functions?

Yes.MySQL computes each window expression independently but in the same scan, so adding RANK(), SUM() OVER() and AVG() OVER() is cost-effective.

Example use cases

• Rank recent orders by value per customer
• Show stock percentage per product
• Calculate 7-day moving revenue average

Performance tip

Index partition and ordering columns to minimize sorting. Avoid large text fields in SELECT if they aren’t required because they increase memory usage during windowing.

Why How to Use Window Functions in MySQL is important

How to Use Window Functions in MySQL Example Usage


-- Running total of customer spend ordered by order_date
SELECT
    o.id,
    o.customer_id,
    o.order_date,
    o.total_amount,
    SUM(o.total_amount) OVER (
        PARTITION BY o.customer_id
        ORDER BY o.order_date
        ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
    ) AS cumulative_spend
FROM Orders o
ORDER BY o.customer_id, o.order_date;

How to Use Window Functions in MySQL Syntax


<pre><code>SELECT
    column_list,
    window_function_name (expression)
        OVER (
            PARTITION BY partition_col1 [, partition_col2]
            ORDER BY order_col1 [ASC|DESC] [, order_col2]
            {ROWS|RANGE} BETWEEN frame_start AND frame_end
        ) AS alias
FROM table_name;

-- Ecommerce ranking example
SELECT
    o.id,
    o.customer_id,
    o.total_amount,
    RANK() OVER (
        PARTITION BY o.customer_id
        ORDER BY o.total_amount DESC
    ) AS order_rank
FROM Orders o;
</code></pre>

Common Mistakes

Using window alias in the same SELECT’s WHERE clause throws an unknown column error. Fix by wrapping the query in a subquery and filtering in the outer layer.
Omitting ORDER BY in the window definition causes non-deterministic results for functions like ROW_NUMBER(). Always specify ORDER BY to guarantee repeatable rankings.