MySQL - Intuitive - 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 FROM
```\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;\n```
['MySQL']