solution to both questions

01-ProductSalesAnalysis-III.sql

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+-- Mock Interview Question 1: Product Sales Analysis III (https://leetcode.com/problems/product-sales-analysis-iii)
+
+with cte as (select product_id, year, quantity, price, 
+dense_rank() over(partition by product_id order by year) as rnk
+from sales)
+select product_id, year as first_year, quantity, price 
+from cte
+where rnk=1

02-CustomersWhoBoughtAllProducts.sql

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+-- Mock Interview Question 2: Customers Who Bought All Products https://leetcode.com/problems/customers-who-bought-all-products
+
+-- solution 1
+
+with 
+p_cte as(
+    select count(product_key) as tot_pdt
+    from product
+),
+c_cte as (
+    select customer_id, count(distinct product_key) as c_pdt
+    from customer group by customer_id
+)
+select customer_id
+from p_cte, c_cte
+where tot_pdt=c_pdt
+
+-- solution 2
+
+select customer_id
+from customer 
+group by customer_id
+having count(distinct product_key) = (select count(product_key) from product)