Если у вас версия 2012+
, то функцию format
можно использовать как:
select concat(nr1, '-', format( cast ( q2.nr2 as int ), '00')) as result
from
(
select substring(q1.str,1,charindex('-',q1.str,1)-1) as nr1,
substring(q1.str,charindex('-',q1.str,1)+1,len(q1.str)) as nr2
from
(
select '3254-1' as str union all
select '3254-25' as str union all
select '3254-6' as str
) q1
) q2;
result
------
3254-01
3254-25
3254-06
Rextester Demo