Скачать или смотреть SQL for Data Science Day 20 | Null Functions | SQL Null Functions | ISNULL | COALESCE | NULLIF

In this lesson, we cover one of the most confusing but MOST important concepts in SQL — NULL values.

You’ll learn how to correctly handle NULLs using the most commonly used SQL Server functions:

✅ What You’ll Learn Today

1️⃣ ISNULL() – Replace NULL with a default value
2️⃣ COALESCE() – Return the first non-NULL value
3️⃣ NULLIF() – Turn matching values into NULL
4️⃣ ISNULL in Calculations – Prevent NULL math errors
5️⃣ COALESCE with Multiple Fallbacks – Smart NULL handling

🧠 IMPORTANT CLARIFICATION

❌ 'Null', ' ', 0, 'NA', 'Unknown' → Not NULL
✔️ NULL → Truly missing value

📊 Sample table used in the video

We work with a Payments table containing Amount, Discount, and CouponCode — with some NULL values.

🧪 Functions you will practice:

Replace NULL with 0

Return first available (non-null) value

Set 0 → NULL using NULLIF

Perform calculations safely

Provide fallback text when coupon is missing

🔥 By the end of this video, you will NEVER be confused by NULLs again!
💬 Ask doubts in comments — I reply to EVERY SQL question.