All 7 Aggregate Functions & GROUP BY questions
More in Aggregate Functions & GROUP BY
How does the GROUP BY clause work together with aggregate functions? How do you filter the results of a grouped query based on an aggregated value, such as only showing customers who spent more than a certain amount? How do you correctly combine WHERE and HAVING in the same query to filter both individual rows and grouped results? What is the difference between COUNT(*), COUNT(1), and COUNT(column_name) in SQL Server? How do the ROLLUP and CUBE extensions to GROUP BY help you generate subtotal and grand total rows in a single query? How would you calculate a running total or a percentage of total using aggregate functions combined with window functions?
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SQL Server › Aggregate Functions & GROUP BY

What are aggregate functions in SQL Server, and what are the most common ones?

Beginner

Answer

Aggregate functions calculate a single summary value from a set of rows, such as counting how many rows exist, adding up a column, or finding the average, minimum, or maximum value. The most common ones are COUNT, SUM, AVG, MIN, and MAX, and they are frequently used to build reports and summaries from large tables.
SELECT COUNT(*) AS TotalOrders, SUM(Amount) AS TotalRevenue, AVG(Amount) AS AverageOrder
FROM Orders;
Real-world example A sales manager runs a query using SUM and AVG to see the total revenue and average order value for the past month, quickly understanding overall sales performance without reviewing every individual order.

Common follow-ups: What is the difference between COUNT(*) and COUNT(column_name)?;Do aggregate functions ignore NULL values by default?

Normalization;Query Optimization & Plans
All 7 Aggregate Functions & GROUP BY questions