find_category_recommendation_pairs.sql

Author: stackcats

database/hard/find_category_recommendation_pairs.sql

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+-- Write your PostgreSQL query statement below
+WITH cte AS (
+    SELECT pp.user_id, pp.product_id, pi.category
+    FROM ProductPurchases pp
+             LEFT JOIN ProductInfo pi ON pp.product_id = pi.product_id)
+SELECT c1.category                category1,
+       c2.category                category2,
+       COUNT(DISTINCT c1.user_id) customer_count
+FROM cte c1
+         LEFT JOIN cte c2 ON c1.user_id = c2.user_id
+WHERE c1.category < c2.category
+GROUP BY c1.category, c2.category
+HAVING COUNT(DISTINCT c1.user_id) > 2
+ORDER BY customer_count DESC, c1.category, c2.category