something like this?

SELECT cast('<root>' + cast(xmlcol1 as nvarchar(max)) + cast(xmlcol2 as nvarchar(max))+'</root>' as xml) FROM yourtable

I don't think the logic works. here is one it would

insert into @tbl1

select col1 Collate Latin1_General_BIN as col1 from

(

select col1, 2 as col2 from @tbl2

union all

select col1,...

I did not check the logic but this fixes your syntax.

insert into @tbl1 select col1 from @tbl2 t2 where not exists (select 1 from @tbl1 where col1 = t2.col1)