Solution : Oracle - UNION
\n/* Write your PL/SQL query statement below */\nSELECT product_id, \n    \'store1\' as store,\n    store1 as price\nFROM products where store1 is not null\nUNI
```\n/* Write your PL/SQL query statement below */\nSELECT product_id, \n    \'store1\' as store,\n    store1 as price\nFROM products where store1 is not null\nUNION \nSELECT product_id, \n    \'store2\' as store,\n    store2 as price\nFROM products where store2 is not null\nUNION\nSELECT product_id, \n    \'store3\' as store,\n    store3 as price\nFROM products where store3 is not null\n```
['Oracle']