RDB$DB_KEY added to "Browse data"

[pgfiore]

Hi guys, sorry for bothering you with such a stupid question... When I "Browse data" (right-click from the tables tree), FR 0.9.11 adds the RDB$DB_KEY pseudo-column to the select statement. It depends on the tables; I mean, it always happens, but only on a few specific tables.
Need help understanding this behavior (if I admit it's really nothing). Thank you
pf

[arvanus]

Does this tables have defined primary key?

[pgfiore]

I've received the whole DB and have yet to investigate the details... And you're right, no PK at all. Thanks for this clue.