SQL Aggregate Functions Cheat Sheet: COUNT, SUM, AVG, GROUP BY & HAVING

Aggregate functions collapse many rows into one value with COUNT, SUM, AVG, MIN, and MAX — the whole result unless you GROUP BY. WHERE filters rows before grouping; HAVING filters groups after. COUNT(*) counts rows, while COUNT(col) ignores NULL in that column.

This SQL cheat sheet is written for people searching for a fast, accurate reference: students, junior developers, and teams shipping production software. Pin it, copy the snippets, and come back when syntax slips.

Quick reference

• COUNT(*): Rows in the group, including NULLs in other columns.
• COUNT(col): Non-NULL values of col.
• SUM / AVG: Ignore NULL. AVG of {10, NULL} is 10, not 5.
• MIN / MAX: Work on numbers, dates, and strings (collation matters).
• GROUP BY: List the non-aggregated SELECT columns.
• HAVING: HAVING COUNT(*) >= 2 after grouping.
• DISTINCT: COUNT(DISTINCT user_id) unique non-null users.
• Filter first: WHERE reduces rows before the aggregate — cheaper and different from HAVING.

Copy-paste examples

Revenue per day with a minimum count

Date grouping functions are dialect-specific; this form is common in MySQL.

SELECT DATE(paid_at) AS day,
       COUNT(*) AS orders,
       SUM(total) AS revenue,
       AVG(total) AS avg_order
FROM orders
WHERE paid_at IS NOT NULL
GROUP BY DATE(paid_at)
HAVING COUNT(*) >= 3
ORDER BY day DESC;

Common mistakes

• Using WHERE COUNT(*) > 1 — aggregates belong in HAVING.
• SUM of a string column and getting 0 or a warning you ignored.
• Forgetting GROUP BY and selecting extra columns (MySQL loose mode).
• Counting a left-joined child with COUNT(*) and inflating parent rows — COUNT(child.id) is safer.

FAQ

1. AVG and empty set? No rows → AVG returns NULL, not 0. Handle that in SQL (COALESCE) or in the app.

1. Can I GROUP BY an alias? MySQL often allows GROUP BY day if day is in SELECT. Strict SQL wants the expression or a subquery. Do not assume portability.

1. Window functions vs GROUP BY? SUM() OVER (PARTITION BY …) keeps row detail. GROUP BY collapses. MySQL 8+ supports windows.

Related SQL cheat sheets

• Sql Cheat Sheet 2026
• Sql Joins Cheat Sheet
• Mysql Vs Sql Cheat Sheet

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