✅ Easy MySQL | UNION
\nselect product_id, \'store1\' as store, store1 as price\nfrom products where store1 is not null\nunion\nselect product_id, \'store2\' as store, store2 as pric
```\nselect product_id, \'store1\' as store, store1 as price\nfrom products where store1 is not null\nunion\nselect product_id, \'store2\' as store, store2 as price\nfrom products where store2 is not null\nunion\nselect product_id, \'store3\' as store, store3 as price\nfrom products where store3 is not null\n```
['Union Find', 'MySQL']