For the other databses that I work with (IBM, ORACLE), when you execute

select max(foo) from bar for update of foo

where foo is of type NUMERIC(18,0). It locks the column foo until a
commit is executed (auto commit is false). ORACLE also allows a
WAIT/NOWAIT parameter at the end which hangs/throws exception
(repectively) if anyone tries to insert or update column foo.

This does not seem to be the case with firebird though the document
seems to suggest that it is supported.

Any light thrown would be much appreciated.

Cheers
-raj