I want to combine 2 column output into one column.
select 1 as id, 2 as exid
id | exid
1 | 2
Unpivot will help you to achieve what you are trying to do
select exprid [id] from (select 1 [id],2 [expid] ) s unpivot (exprid for col in (id,expid)) as t2
Compared to the using union this should be faster because it will only scan the table once instead of twice.