select title
Case when catloglevelid ='123' Then 1- title
Else 2- title As [Level]
from catalog_time_table
You will get can not convert introductory nvarchar to int Error.
To fix this error, just do one thing
select title
Case when catloglevelid ='123' Then '1-' + title
Else '2-' + title As [Level]
from catalog_time_table