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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.

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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