very easy sql query using union
\nselect product_id,\'store1\' as store,store1 as price from Products where store1 is not null\nunion\nselect product_id,\'store2\' as store,store2 as price fro
```\nselect product_id,\'store1\' as store,store1 as price from Products where store1 is not null\nunion\nselect product_id,\'store2\' as store,store2 as price from Products where store2 is not null\nunion\nselect product_id,\'store3\' as store,store3 as price from Products where store3 is not null```
['MySQL']