Use of (primary) key in internal tables

Hi,

this question is for the real experts (like Horst Keller) so please don't answer if not really know...

I delare an internal table with various fields as SORTED TABLE WITH UNIQUE KEY table_line - I won't have any duplicates as I fill from a database (customizing) table.

In a LOOP AT this table WHERE <field> = <value>, will the loop use the key if it's the first key?

What are the rules of index use in LOOP?

I mean NOT secondary index as they can be defined now.

Thanks a lot and best regards,

Clemens