FB does not catch ambiguous column names in a sub-query. For example,
I want find all passengers who are boarding flights on a certain date
at a certain point on the route:

select PersonnelNo
from Passenger P
inner join Flight F on P.FltSeqNo = F.FltSeqNo
where FltDate = current_date
and DepartFrom = ?

There is a DepartFrom column in both tables so FB raises an exception.
However if I have the same SQL in a sub-query there is no objection:

select ...
where PersonnelNo in
(select PersonnelNo
from Passenger P
inner join Flight F on P.FltSeqNo = F.FltSeqNo
where FltDate = current_date
and DepartFrom = ?)

A small point but I am converting form InterBase and am getting
paranoid about ambiguous column names.

Dave