My simple MySQL solution
\nSELECT c.customer_id\nFROM Customer c\nGROUP BY c.customer_id\nHAVING COUNT(DISTINCT product_key) = (SELECT COUNT(DISTINCT product_key) FROM Product p)\n
```\nSELECT c.customer_id\nFROM Customer c\nGROUP BY c.customer_id\nHAVING COUNT(DISTINCT product_key) = (SELECT COUNT(DISTINCT product_key) FROM Product p)\n```
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