SQL Aggregate Functions

SQL Aggregate Functions

Aggregate functions perform calculations on a set of rows and return a single value. They are commonly used for reporting and data analysis.

Common Aggregate Functions

• COUNT() – returns the number of rows
• SUM() – returns the total of a numeric column
• AVG() – returns the average value
• MIN() – returns the smallest value
• MAX() – returns the largest value

COUNT Example

SELECT COUNT(*) AS total_customers
FROM customers;

SUM Example

SELECT SUM(price) AS total_revenue
FROM orders;

AVG Example

SELECT AVG(price) AS average_price
FROM products;

MIN and MAX Example

SELECT MIN(price) AS lowest_price,
       MAX(price) AS highest_price
FROM products;

Aggregate Functions and NULL

Most aggregate functions ignore NULL values. For example, AVG() does not count NULL values in its calculation.

Using WHERE with Aggregates

You can filter rows before aggregation using WHERE.

SELECT COUNT(*) AS active_customers
FROM customers
WHERE status = 'active';

Grouping Data

To calculate aggregates per category, country, or group, use GROUP BY (covered in detail later).

SELECT country, COUNT(*) AS total_customers
FROM customers
GROUP BY country;

Common Mistakes

• Forgetting GROUP BY when selecting non-aggregated columns
• Misunderstanding how NULL values affect results
• Using COUNT(column) vs COUNT(*) without knowing the difference

Next Step

Continue with SQL MIN and MAX for a deeper look at value comparison functions.