Can you provide more info on input & desired output?

RegEx would be nice in T-SQL ... but here's an an example implementing what HanShi recommended:

CREATE FUNCTION AlphaNum (@s varchar(100))

RETURNS varchar(100) AS

BEGIN

Declare @n int = PatIndex('%[^A-Z0-9]%', @s-2);

While @n...

Another option:

SELECTname, CASE

WHEN Mark1>Mark2 AND Mark1>Mark3 THEN 'Mark1'

WHEN Mark2>Mark3 THEN 'Mark2'

ELSE 'Mark3' END

FROMSample;