Select max value from different column in a row in oracle database

Question

My table in oracle database is like this:

Rollno  |   mark1   |   Mark2   |   mark3
--------+-----------+-----------+--------+
101     |   10      |   20      |   30
102     |   22      |   44      |   08
103     |   55      |   11      |   14
--------+-----------+-----------+--------+

And I want output like

Rollno  |   MAX(Mark1,mark2,mark3)
--------+-------------------------+
101     |   30
102     |   44
103     |   55
--------+-------------------------+

Any query suggestion?

Answer 1

Use GREATEST function

SELECT Rollno, GREATEST (mark1, Mark2, mark3) AS Maxv
FROM yourtable

Answer 2

ANSI SQL compliant answer, written before Oracle was specified:

Use CASE to find largest column value:

select Rollno, case when mark1 > mark2 and mark1 > mark3 then mark1
                    when mark2 > mark3 then mark2
                    else mark3 end as max_value
from tablename

( NULL 's not considered here.)