Medium LC problem = CustomersWhoBoughtAllProducts.sql

LeetCode/SQL50/CustomersWhoBoughtAllProducts.sql

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+-- Table: Customer
+
+-- +-------------+---------+
+-- | Column Name | Type    |
+-- +-------------+---------+
+-- | customer_id | int     |
+-- | product_key | int     |
+-- +-------------+---------+
+-- This table may contain duplicates rows. 
+-- customer_id is not NULL.
+-- product_key is a foreign key (reference column) to Product table.
+
+-- Table: Product
+
+-- +-------------+---------+
+-- | Column Name | Type    |
+-- +-------------+---------+
+-- | product_key | int     |
+-- +-------------+---------+
+-- product_key is the primary key (column with unique values) for this table.
+
+-- Write a solution to report the customer ids from the Customer table that bought all the products in the Product table.
+
+-- Return the result table in any order.
+
+-- The result format is in the following example.
+
+-- Example 1:
+
+-- Input: 
+-- Customer table:
+-- +-------------+-------------+
+-- | customer_id | product_key |
+-- +-------------+-------------+
+-- | 1           | 5           |
+-- | 2           | 6           |
+-- | 3           | 5           |
+-- | 3           | 6           |
+-- | 1           | 6           |
+-- +-------------+-------------+
+-- Product table:
+-- +-------------+
+-- | product_key |
+-- +-------------+
+-- | 5           |
+-- | 6           |
+-- +-------------+
+-- Output: 
+-- +-------------+
+-- | customer_id |
+-- +-------------+
+-- | 1           |
+-- | 3           |
+-- +-------------+
+-- Explanation: 
+-- The customers who bought all the products (5 and 6) are customers with IDs 1 and 3.
+
+-- Write your PostgreSQL query statement below
+-- Solution
+with products_count as (
+    select count(product_key) as num_products from Product
+)
+select customer_id from (
+    select customer_id,
+        count(distinct product_key) as num_products_bought
+    from Customer group by customer_id
+) tb where tb.num_products_bought in (
+    select num_products from products_count
+);