Is order by clause allowed in a subquery

Question

Is there any reason why or why not you should do an \'order by\' in a subquery?

Answer 1

Unless you use top it is not useful since you will be ordering in the outer query anyway

Answer 2

No ORDER BY is valid in a subquery when you are interested in a subset of the overall data, hence you always need a TOP (SQL Server). There's no point having an ORDER BY without TOP in a subquery because the overall ordering of the results is handled by the outer query.

Answer 3

Depending on the size of the sub-query, it will impact performance to a varrying degree.

Order shouldn't matter on a sub-query though. You should be able to move the Order By portion to the Outer Query (which should be the one returning the final results).