Ask a few super simple SQL statements:

wgfxman

top 20 percent @departtotal
The top 20 percent is only valid for the entire query result (select sum (number) from table name)

And (select sum (number) from table name) will only return one record, so the result is the same

pguppgdn

declare @departtotal int
select @departtotal =sum(number) from (select top 20 percent sum(number) from table name) a

lancelover

Well, I learned a bit