What Are Aggregate Functions in SQL? Learn with Examples

Tutorials • 07-Aug-2025

by Roxana Haidiner

Aggregation functions are like mini-calculators inside your database.

Instead of showing each row one by one, they let you perform a calculation across multiple rows, and return just one result.

They’re often used with the GROUP BY clause, which splits the data into smaller groups (like per customer or per product), so you can get one result per group.

Here are the most common SQL aggregation functions:

Function	What It Does
`MIN()`	Returns the smallest value in the column
`MAX()`	Returns the highest value in the column
`COUNT()`	Counts how many rows are present (ignores `NULL`, unless using `COUNT(*)`)
`SUM()`	Adds up all values in a numeric column
`AVG()`	Calculates the average of all numeric values

In the next section, we’ll show you each one with examples - both in plain SQL and visually using DbSchema.

Let’s Start with a Simple Example

Imagine this orders table:

order_id	customer_id	product_name	total_amount
1	101	Juice	25.00
2	102	Cereal	32.50
3	101	Bread	45.00
4	103	Milk	28.00

Each row is one order. For example, customer 101 placed two orders: one for Juice and one for Bread.

1. How many orders do we have?

SELECT COUNT(*) FROM orders;

Returns:

count
4

2. What is the total revenue?

SELECT SUM(total_amount) FROM orders;

Returns:

sum
130.50

3. What is the average order value?

SELECT AVG(total_amount) FROM orders;

Returns:

avg
32.625

4. What is the lowest order value?

SELECT MIN(total_amount) FROM orders;

Returns:

min
25.00

5. What is the highest order value?

SELECT MAX(total_amount) FROM orders;

Returns:

max
45.00

GROUP BY - Summarize by Category

If you want to know how much each customer spent in total, you can use GROUP BY:

SELECT customer_id, SUM(total_amount)
FROM orders
GROUP BY customer_id;

This returns:

customer_id	sum
101	70.00
102	32.50
103	28.00

So now you know that:

Customer 101 bought Juice and Bread, spending a total of $70.00.
Customer 102 bought Cereal, spending $32.50.
Customer 103 bought Milk, spending $28.00.

Note: Aggregation functions skip over NULL values when doing their calculations - except for COUNT(), which counts all rows, including those with NULLs.

️ Improved Method: Do All of This Visually in DbSchema

You don’t even have to write SQL by hand. Instead, you can use a visual database tool like DbSchema.

In the Query Builder, you can create aggregation queries using just a few clicks - no SQL coding required.

SQL Aggregation Functions

This screenshot shows how to calculate the total amount spent by each customer, step by step, using DbSchema’s visual Query Builder - no SQL needed.

How to Use the Query Builder

Open the Query Builder Launch DbSchema and go to the Query Builder tab.
Add the Table Drag your orders table into the builder area.
Pick the Columns
- Check the box for customer_id
Apply an Aggregation
- Right-click on total_amount
- Hover over Aggregate
- Choose SUM(), AVG(), MIN(), or any other function you need
Group the Results DbSchema will automatically group by any columns that are not aggregated - in this case, customer_id.
Run the Query Click Run to see the results instantly.

Tip: DbSchema also shows you the SQL it generates, so you can learn while building your queries visually.

SQL Aggregation Functions Query Results

Why Aggregation Functions Matter

Aggregation helps you see the big picture in your data:

Total sales
Average ratings
Most frequent values
Summaries per group (customers, regions, products)

Whether you're analyzing data for school, work, or just exploring - these functions help you understand what’s really happening inside your database.

Final Thoughts

Aggregation functions are some of the most useful, and beginner-friendly features in SQL. And when you use a visual builder like DbSchema, you don’t need to memorize syntax or write code.