Simple | easy | MYSQL
<<< Press Upvote Button !!!!!!\n\n\n# Write your MySQL query statement below\n\nselect product_id , ( \'store1\' ) as store , store1 as price\n    from Products
**<<< Press Upvote Button !!!!!!**\n\n```\n# Write your MySQL query statement below\n\nselect product_id , ( \'store1\' ) as store , store1 as price\n    from Products where store1 is NOT NULL\n    \nUNION\n\nselect product_id , ( \'store2\' ) as store , store2 as price\n    from Products where store2 is NOT NULL\n    \nUNION\n\nselect product_id , ( \'store3\' ) as store , store3 as price\n    from Products where store3 is NOT NULL;\n```\n![image](https://assets.leetcode.com/users/images/b9f113a0-064b-4cf7-ab09-6154212b13ef_1654975841.638725.jpeg)\n
['Union Find', 'MySQL']