SQL Server 2017

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

create table TestAmount
(
    Amount1 int,
    Amount2 int,
    Amount3 int,
    MaxValuedata as (CASE WHEN Amount1>Amount2 AND Amount1>Amount3 THEN Amount1
                          WHEN Amount2>Amount3                     THEN Amount2
                                                                   ELSE Amount3
                     END)
)
INSERT INTO TestAmount (Amount1, Amount2, Amount3)
VALUES
(1,2,3),
(2,3,1),
(3,1,2)
3 rows affected

select * from testamount


Amount1
Amount2
Amount3
MaxValuedata


1
2
3
3

2
3
1
3

3
1
2
3