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?" 💡

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🌟 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). 💰

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💻 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;

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💻 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';

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🎨 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)

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📈 Learning Path

• ← Back: Aggregates Hub
• Next: MIN & MAX Functions →