MySQL Solution || Union of Tables
\n\tSELECT product_id, \'store1\' AS store, store1 AS price \n\tFROM Products \n\tWHERE store1 IS NOT NULL\nUNION\n\tSELECT product_id, \'store2\' AS store, sto
```\n\tSELECT product_id, \'store1\' AS store, store1 AS price \n\tFROM Products \n\tWHERE store1 IS NOT NULL\nUNION\n\tSELECT product_id, \'store2\' AS store, store2 AS price \n\tFROM Products \n\tWHERE store2 IS NOT NULL\nUNION\n\tSELECT product_id, \'store3\' AS store, store3 AS price \n\tFROM Products \n\tWHERE store3 IS NOT NULL\n```
['Union Find', 'MySQL']