Difference beween Rank(), Dense_Rank(), Row number()

DECLARE @OrderRanking AS TABLE

(

OrderID INT IDENTITY(1,1) NOT NULL,

CustomerID INT,

OrderTotal decimal(15,2)

)

INSERT into @OrderRanking (CustomerID, OrderTotal)

SELECT 1, 1000

UNION ALL

SELECT 1, 500

UNION ALL

SELECT 1, 650

UNION ALL

SELECT 1, 650

UNION ALL

SELECT 1, 3000

UNION ALL

SELECT 2, 1000

UNION ALL

SELECT 2, 2000

UNION ALL

SELECT 2, 500

UNION ALL

SELECT 2, 500

UNION ALL

SELECT 3, 500

UNION ALL

SELECT 3, 20

SELECT * FROM @OrderRanking

SELECT *,

ROW_NUMBER() OVER (ORDER BY OrderTotal DESC) AS RN,

ROW_NUMBER() OVER (PARTITION BY CustomerID ORDER BY OrderTotal DESC) AS RNP,

RANK() OVER (ORDER BY OrderTotal DESC) AS R,

RANK() OVER (PARTITION BY CustomerID ORDER BY OrderTotal DESC) AS RP,

DENSE_RANK() OVER (ORDER BY OrderTotal DESC) AS DR,

DENSE_RANK() OVER (PARTITION BY CustomerID ORDER BY OrderTotal DESC) AS DRP

FROM @OrderRanking