SOLUTION USING UNION
\nselect product_id,\'store1\' as store,store1 as price\nfrom Products\nwhere store1 is not null\n\n\nunion\n\n\nselect product_id,\'store2\' as store,store2 as
```\nselect product_id,\'store1\' as store,store1 as price\nfrom Products\nwhere store1 is not null\n\n\nunion\n\n\nselect product_id,\'store2\' as store,store2 as price\nfrom Products\nwhere store2 is not null\n\n\nunion\n\n\nselect product_id,\'store3\' as store,store3 as price\nfrom Products\nwhere store3 is not null\n```
['Union Find', 'MySQL']