Aggregate Functions

Aggregate functions perform a calculation across multiple rows and return a single summary value - essential for turning raw rows of data into meaningful totals, averages, and counts.

Common Aggregate Functions

• COUNT() - counts the number of rows
• SUM() - adds up numeric values
• AVG() - calculates the average of numeric values
• MIN() - finds the smallest value
• MAX() - finds the largest value

Examples

-- Total number of customers
SELECT COUNT(*) FROM customers;

-- Total revenue across all orders
SELECT SUM(amount) FROM orders;

-- Average order amount
SELECT AVG(amount) FROM orders;

-- Highest and lowest order amounts
SELECT MAX(amount), MIN(amount) FROM orders;

Aggregates with WHERE

-- Total revenue from Noida customers only
SELECT SUM(o.amount)
FROM orders o
JOIN customers c ON o.customer_id = c.customer_id
WHERE c.city = 'Noida';