🧠 SQL Interview Question (Commonly Asked)
📌

orders(order_id, customer_id, order_date, order_amount)

❓ Ques :

👉 Find customers whose order amount strictly increased compared to their previous order.

🧩 How Interviewers Expect You to Think

• Order data correctly using dates
• Compare current row with previous row
• Use window functions for self-comparison
• Avoid self-joins when window functions fit better
• Filter only after comparison logic

💡 SQL Solution

WITH ranked_orders AS (
SELECT
customer_id,
order_date,
order_amount,
LAG(order_amount) OVER (
PARTITION BY customer_id
ORDER BY order_date
) AS prev_order_amount
FROM orders
)
SELECT DISTINCT
customer_id
FROM ranked_orders
WHERE order_amount > prev_order_amount;

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