SQL COUNT & SUM Functions 🧮¶

Mentor's Note: COUNT and SUM are the most basic reporting tools. COUNT tells you "How many?" and SUM tells you "How much?" 💡

🌟 The Scenario: The T-Shirt Shop 👕¶

Imagine you are managing an inventory. - COUNT: "How many orders did we receive today?" (The number of rows). 📦 - SUM: "What was the total money earned from those orders?" (The sum of the 'Price' column). 💰

💻 1. The COUNT() Function¶

Counts the number of records in a set.

A. COUNT(*) vs COUNT(column)¶

COUNT(*): Counts every row, including those with NULL values.
COUNT(column): Counts only the rows where that specific column is NOT NULL.

-- Scenario: Total number of records
SELECT COUNT(*) FROM orders;

-- Scenario: Count people who have an email registered
SELECT COUNT(email) FROM customers;

B. COUNT(DISTINCT)¶

Counts unique values only.

-- Scenario: How many different cities do we ship to?
SELECT COUNT(DISTINCT city) FROM orders;

💻 2. The SUM() Function¶

Adds up all the numeric values in a column.

-- Scenario: Total revenue for February
SELECT SUM(total_price) 
FROM orders
WHERE order_date BETWEEN '2026-02-01' AND '2026-02-28';

🎨 Visual Logic: Count vs Sum¶

Order ID	Product	Qty
1	Pen	10
2	Pencil	20
3	Notebook	NULL

COUNT(Qty) = 2 (Ignores the NULL)
SUM(Qty) = 30 (10 + 20)