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1. What Are Aggregate Functions?

Aggregate functions return a single value by processing multiple rows of data.

They're used in reports, dashboards, and any place where you need summaries like totals, averages, or counts.

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2. Common Aggregate Functions

Function	Purpose	Example Usage
SUM()	Adds up values in a column	SUM(salary)
COUNT()	Counts rows or non-null values	COUNT(*), COUNT(name)
AVG()	Calculates the average value	AVG(grade)
MAX()	Finds the highest value	MAX(score)
MIN()	Finds the lowest value	MIN(price)

These are all used inside a SELECT statement.

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3. Example: Total Sales

Assume you have a table called sales with the following data:

id	amount
1	100
2	200
3	300

Create table

CREATE TABLE sales (
  id INT PRIMARY KEY,
  amount INT
);

The total sales can be calculated using the SUM() function.

SELECT SUM(amount)
FROM sales;

This returns the total amount sold across all rows in the sales table.

Result

600

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4. Where Are Aggregates Used?

Aggregate functions work well with:

• GROUP BY (to break totals by category)
• HAVING (to filter groups by their total or average)

We'll cover both in more detail with examples later in this chapter.

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5. Key Use Cases

You might use aggregation to:

• Calculate total revenue
• Count users who signed up this month
• Find the lowest price in stock
• Track average order value

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