Easy solution with union
\n  SELECT PRODUCT_ID, \'store1\' AS STORE, STORE1 AS PRICE\n    FROM PRODUCTS\n   WHERE STORE1 IS NOT NULL    \n   UNION\n  SELECT PRODUCT_ID, \'store2\' AS ST
```\n  SELECT PRODUCT_ID, \'store1\' AS STORE, STORE1 AS PRICE\n    FROM PRODUCTS\n   WHERE STORE1 IS NOT NULL    \n   UNION\n  SELECT PRODUCT_ID, \'store2\' AS STORE, STORE2 AS PRICE\n    FROM PRODUCTS\n   WHERE STORE2 IS NOT NULL    \n   UNION\n  SELECT PRODUCT_ID, \'store3\' AS STORE, STORE3 AS PRICE\n    FROM PRODUCTS\n   WHERE STORE3 IS NOT NULL\n   ```
['Union Find', 'MS SQL Server']