Easy Mysql Solution
select * from\n(select product_id, \'store1\' as store, store1 as price from Products\nunion\nselect product_id, \'store2\' as store, store2 as price from Produ
select * from\n(select product_id, \'store1\' as store, store1 as price from Products\nunion\nselect product_id, \'store2\' as store, store2 as price from Products\nunion\nselect product_id, \'store3\' as store, store3 as price from Products) t\nwhere price is not null
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