Tip: SQL Window Functions are a Game Changer

Learning Exchange
1

Window functions perform a calculation across a set of table rows that are somehow related to the current row.

Unlike GROUP BY, they don’t collapse rows.

ROW_NUMBER() is a great place to start. It assigns a unique integer to each row within a partition.

Example: Find the most recent login for each user.

SELECT * FROM (
    SELECT
        UserID,
        LoginDate,
        ROW_NUMBER() OVER(PARTITION BY UserID ORDER BY LoginDate DESC) as rn
    FROM UserLogins
) as subquery
WHERE rn = 1;

This is perfect for ranking, identifying duplicates, or finding the “first” or “last” of something for each customer/product/region without complex self-joins.

What’s the impact? You can now easily identify a customer’s first purchase or their most recent support ticket.

How have you used window functions? Let’s discuss!

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