Customers who bought all products

#
# 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 MySQL query statement below

SELECT customer_id
FROM Customer
GROUP BY customer_id
HAVING COUNT(DISTINCT product_key) = (SELECT COUNT(*) FROM Product);