✅✅ MYSQL || Union || Efficient Approach || Easy to understand
*Please Upvote if you found this helpful.*\n\n\n\nselect product_id,\'store1\' as store,store1 as price from Products\nwhere store1 is not null\n\nunion\n\nsele
****Please Upvote if you found this helpful.****\n\n\n```\nselect product_id,\'store1\' as store,store1 as price from Products\nwhere store1 is not null\n\nunion\n\nselect product_id,\'store2\' as store,store2 as price from Products\nwhere store2 is not null\n\nunion\n\nselect product_id,\'store3\' as store,store3 as price from Products\nwhere store3 is not null\norder by product_id asc,price desc;\n```
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