General questions about query layers how to copy query layers

I am trying to wrap my head around the difference between database views and query layers.

• What is the difference between a database view and a query layer?
• How can I tell if a layer/table in my SDE database is a view or a query layer?
• Can someone explain why I get a different number of features in my Attribute table depending on which unique identifier field I use when adding the query layer to my MXD in ArcMAP? Will I only get as many features as there are unique values in the field I choose?
• If I open the Attribute table of a query layer in ArcMAP, and then sort a column, the number of features change. Why?

Secondly: I would like to copy the contents of a query layer from an SDE database to a GDB. I see that this page tells you to add the query layer to an MXD and then to export the data to a feature class. But we would like to use FME to export the contents of the query layer to a GDB.

• If I copy the query layer from the SDE database and paste it in a GDB: how do I know which Unique identifier field has been chosen? Are the results unpredictable, is that why you should export the data from an MXD to a feature class?

Thanks in advance!

Turid