MySQL Solution
Intuition\n Describe your first thoughts on how to solve this problem. \n\n# Approach\n Describe your approach to solving the problem. \n\n# Complexity\n- Time 
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\n\n# Approach\n<!-- Describe your approach to solving the problem. -->\n\n# Complexity\n- Time complexity:\n<!-- Add your time complexity here, e.g. $$O(n)$$ -->\n\n- Space complexity:\n<!-- Add your space complexity here, e.g. $$O(n)$$ -->\n\n# Code\n```\n# Write your MySQL query statement below\nSELECT product_id, \'store1\' AS store, store1 AS price \nFROM Products \nWHERE store1 IS NOT NULL\nUNION \nSELECT product_id, \'store2\' AS store, store2 AS price \nFROM Products \nWHERE store2 IS NOT NULL\nUNION \nSELECT product_id, \'store3\' AS store, store3 AS price \nFROM Products \nWHERE store3 IS NOT NULL\n```
['MySQL']