Hi,
I am not getting, why are you using sub-query? Your simple query will work and give the required output.
select top 100 percent 1 as t,t1.regId, t1.visitCount from registerdata as t1 order by t1.visitCount desc
Also check below query if you are using union...
now try this....just added desc with 1 in order by clause.
select top 100 percent 1 as t,t1.regId, t1.visitCount from registerdata as t1
union
select top 100 percent 2 as t,t2.regId, t2.visitCount from table2 as t2
order by 1 desc , 3 desc
Hope this will help you.