Leon,

L> 1.is it a kind of record locking (if your where clause collects only 1
L> record ) ?

actually it locks all the records retrieved (if it can) as it fetches
them; usually you'll want to use it on a single-record select, but that's not
mandatory.

L> 2.does it lock all fields in the where clause or complete records

it locks the record; Firebird (nor any other RDBMS that I know) cannot
lock single columns.

L> 2.how long are records locked ? until post or until commit ?

I think locks are released upon transaction end (commit or rollback).

L> 3.is it an alternative for thoe old recordlocking ?

If you mean "dummy updates", then yes, with the additional benefits of
greater efficiency and update triggers not firing twice.

The behaviour of this feature varies with the transaction isolation
level and flags (like wait/no_wait) you use; see the release notes and
the archives of the firebird-devel list to know more.

Ciao
--
Nando mailto:nandod@...