Customers Who Bought All Products

Task: Write a solution to report the customer ids from the Customer table that bought all the products in the Product table.

Table: Customer

+-------------+------+
| Column Name | Type |
+-------------+------+
| customer_id | INT  |
| product_key | INT  |
+-------------+------+

Table: Product

+-------------+------+
| Column Name | Type |
+-------------+------+
| product_key | INT  |
+-------------+------+

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           |
+-------------+