🎯 SQL Interview Pattern: Running Total (Cumulative Sum)

Master this one pattern, and you'll be able to solve questions like:

📈 Running Total of Sales
💰 Cumulative Revenue
🛒 Customer Lifetime Spend
📦 Running Inventory Balance
👥 Cumulative User Sign-ups
💳 Account Balance After Each Transaction
📊 Cumulative Monthly Profit

🧠 How to Identify This Pattern

If the question contains words like:

• Running Total
• Cumulative
• Till Date
• So Far
• Progressive Sum
• Rolling Balance

👉 Think: Window Function (SUM() OVER())

✅ Approach

1️⃣ Identify the value to accumulate.
2️⃣ Find the correct ordering column (usually Date or ID).
3️⃣ Use:

SUM(column_name) OVER (
ORDER BY column_name
)

💡 Bonus Tip:

Need a separate running total for each customer, product, or department?

➡️ Add PARTITION BY before ORDER BY.

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