WITH CTE AS (
SELECT [User],GWP,
       ROW_NUMBER() OVER(PARTITION BY [User] ORDER BY GWP DESC) AS rn
FROM MyTable)
SELECT [User],GWP
FROM CTE
WHERE rn=1;

WITH CTE AS (
SELECT [User],GWP,
       ROW_NUMBER() OVER(PARTITION BY [User] ORDER BY GWP DESC) AS rn
FROM MyTable)
SELECT [User],GWP
FROM CTE
WHERE rn=1;

SELECT
    [User], MAX(GMP)
FROM MyTable
GROUP BY
    [User]

CREATE TABLE dbo.Users
(
    UserName        varchar(50) NOT NULL,
    MiddleColumn    integer NOT NULL,
    GWP             money NOT NULL
);

INSERT dbo.Users
    (UserName, MiddleColumn, GWP)
SELECT 'Salesperson A', 23171, 320230.00 UNION ALL
SELECT 'Salesperson B', 11782, 199584.00 UNION ALL
SELECT 'Salesperson C', 16769, 14437175.00 UNION ALL
SELECT 'Salesperson D', 17191, -635580.00 UNION ALL
SELECT 'Salesperson A', 16844, 122000.00 UNION ALL
SELECT 'Salesperson B', 18708, 159775.00 UNION ALL
SELECT 'Salesperson D', 10969, 225295.00 UNION ALL
SELECT 'Salesperson C', 18681, 73040.00 UNION ALL
SELECT 'Salesperson D', 26480, 768201.00 UNION ALL
SELECT 'Salesperson A', 10310, -111325.00 UNION ALL
SELECT 'Salesperson B', 17291, -460550.00 UNION ALL
SELECT 'Salesperson B', 11116, 323329.00 UNION ALL
SELECT 'Salesperson E', 19162, -65940.00 UNION ALL
SELECT 'Salesperson C', 11224, 947025.00 UNION ALL
SELECT 'Salesperson A', 10568, 73040.00;

SELECT * 
FROM dbo.Users AS u
WHERE
    GWP =
    (
    SELECT
        MAX(u2.GWP) AS MaxGWP
    FROM dbo.Users AS u2
    WHERE
        u2.UserName = u.UserName
    )

Select U.* from dbo.Users U with (Nolock)
Join (Select username, MAX(GWP) MGWP from dbo.Users with (Nolock)
Group by username) as A
on A.UserName=u.UserName and A.MGWP=U.GWP 

SELECT 
    U.* 
FROM dbo.Users AS U
JOIN 
(
    SELECT 
        U2.UserName, 
        MAX(U2.GWP) AS MGWP 
    FROM dbo.Users AS U2
    GROUP BY 
        U2.UserName
) AS A ON
    A.UserName = U.UserName 
    AND A.MGWP = U.GWP