Detection of which attributes should get set in update trigger

On Friday, November 10, 2023, Thiemo Kellner <thiemo@gelassene-pferde.biz>
wrote:

Hi all

I have a view, that is a join over 4 tables (the setup of the rule
question). I want to update the central table over the view (by an
instead-of trigger). How can I determine, whether an attribute should get
set to NULL, "new.XYZ is null" or whether it should be left alone. Is there
a leave-me-alone function determining, whether an attribute is in the set
clause of an update statement. I am thinking along the line code in the
trigger function like

update TABLE
set XYZ = case
when leave-me-alone (new.XYZ) then old.XYZ
else new.XYZ
end;

And what about the where condition... hm, guess I am a bit confused.

IIUC, The NEW record is complete, with every value as it should be in the
newly saved tuple. There is no leave-me-alone concept. You don’t get to
know if the column was specified or not in the update command.

David J.

Thanks for the reply. I confirm the behaviour. Your explanation makes
sense if I consider having read that with an update the is a complete
new record version written.

Am 10.11.2023 um 14:35 schrieb David G. Johnston: