How to check if a column is being updated

Let’s suppose I have an instruction that does the following:

update client set active = 0;

Is there any way to do it in Firebird, the same thing as Oracle does …

if updating (active) ...

The trigger would only be executed if it had only only updating the “active” column.

I tried that way, but it’s not working:

CREATE OR ALTER TRIGGER CLIENT_SYNC FOR CLIENT
ACTIVE BEFORE INSERT OR UPDATE POSITION 0
as begin   
    IF UPDATE(ACTIVE)   
        new.ACTIVE = NULL;
end;

Answer

Firebird doesn’t have anything like updating. You need to compare the previous value (in the old context variable) with the new value (in the new context variable), preferably using is distinct from to avoid issues with null:

set term #;
CREATE OR ALTER TRIGGER CLIENT_SYNC FOR CLIENT
ACTIVE BEFORE INSERT OR UPDATE POSITION 0
as 
begin   
    IF (old.active is distinct from new.active) then  
        new.ACTIVE = NULL;
end#
set term ;#

The update of by setting new.ACTIVE = null seems a bit odd in the context, but I assume that is just a placeholder (otherwise ACTIVE can never by anything other than null).

And be sure to consult the Firebird documentation on procedural SQL, as the code in your question has several other syntax errors.