MSSQL answer
\nSELECT   customer_id\nFROM     Customer\nGROUP BY customer_id\nHAVING   COUNT(DISTINCT product_key) = (SELECT COUNT(DISTINCT product_key)FROM Product)\n\n
```\nSELECT   customer_id\nFROM     Customer\nGROUP BY customer_id\nHAVING   COUNT(DISTINCT product_key) = (SELECT COUNT(DISTINCT product_key)FROM Product)\n```\n
['MS SQL Server']