Derivation in data stream or in select statement?

[Nico1984]

Could somebody explain me the difference in performance between a derivation in the datastream and a derivation, written in SQL, in the select statement?

Thanks

[Blue]

As I understand it the former is done by the Data Manager tool AFTER the data has been read from the database and the latter is done at the database and read by Data Manager as database metadata.

Bluey