Simple MySQL Solution
Simple join and group by, followed by selecting customers whose unique(distinct) product bought count is equal to total number of products in product table.\n\n
Simple join and group by, followed by selecting customers whose unique(distinct) product bought count is equal to total number of products in product table.\n\n```\nselect customer_id\nfrom Customer \ngroup by customer_id\nhaving count(distinct(product_key)) = (select count(product_key) from Product)\n```
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