No subquery simple MySQL solution (count distinct)
\nselect customer_id\nfrom customer \ngroup by customer_id \nhaving count(distinct product_key) = (select count(distinct product_key) from product)\n\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\n
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