Using UNPIVOT
select product_id,store,price from Products\nUNPIVOT\n(\n    price \n    for store in (store1,store2,store3)\n) as unpivoting
select product_id,store,price from Products\nUNPIVOT\n(\n    price \n    for store in (store1,store2,store3)\n) as unpivoting
['MS SQL Server']