🧠 SQL Interview Question (Products Frequently Bought Together)
📌

order_items(order_id, product_id)

❓ Ques :

👉 Find pairs of products that are frequently bought together in the same order

👉 Return product_id_1, product_id_2, pair_count

🧩 How Interviewers Expect You to Think

• Self-join on same order 🛒
• Avoid duplicate/reverse pairs
• Count frequency of each pair

💡 SQL Solution

SELECT
o1.product_id AS product_id_1,
o2.product_id AS product_id_2,
COUNT(*) AS pair_count
FROM order_items o1
JOIN order_items o2
ON o1.order_id = o2.order_id
AND o1.product_id < o2.product_id
GROUP BY
o1.product_id,
o2.product_id
ORDER BY pair_count DESC;

🔥 Why This Question Is Powerful

• Classic market basket analysis 🧠
• Tests self-join + combinations logic
• Frequently asked in e-commerce & analytics roles

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