order by clause will not accept the negative number.
if you are trying to give
select * from sys.indexes order by -1 desc
it wont accept, it will give you the following error
Msg 108, Level 16, State 1, Line 1
The ORDER BY position number -1 is out of range of the number of items in the select list.
Here you are ordering by the type desc column and the type_desc column contains the negative values. So It a negative data. In that case it will accept that.
Check the following query, you will get a clear picture.
select case type_desc when 'clustered' then -1 else type end, * from sys.indexes
order by case type_desc when 'clustered' then -1 else type end desc
here see the first column, you can understand how the sql server engine has sorted.
