Selective Auto-Timestamp [using triggers?]

Rajit Singh writes:

The thing is, I also want to be able to update the timestamp field
if I want to...

Here's my solution:

CREATE FUNCTION updated_stamp () RETURNS OPAQUE AS
' BEGIN
IF NEW.updated ISNULL THEN
NEW.updated := ''now'';
END IF;
RETURN NEW;
END;
' LANGUAGE 'plpgsql';

Change:

if old.modtime = new.modtime

To:

if new.modtime is null

I *think* that's what you are looking for.

--rob

----- Original Message -----
From: "Rajit Singh" <singh.raj@studychoice.com>
To: <pgsql-general@postgresql.org>
Sent: Thursday, January 11, 2001 7:00 AM
Subject: Selective Auto-Timestamp [using triggers?]

Dear List,

I've recently found that it would be useful if I could update a timestamp

field in some of my tables automatically so that whenever someone updates
the tables in question, the timestamp reflects when that change was made.

The thing is, I also want to be able to update the timestamp field if I

want to... thus if I update, say, the 'name' field - the timestamp field
would be updated to 'now()'. However, if I updated the timestamp field then
that field would simply take on the value I had suggested.

I managed to find a partially working solution as follows:

CREATE FUNCTION update_modtime() RETURNS opaque AS 'BEGIN IF OLD.modtime =

NEW.modtime THEN NEW.modtime = now() END IF; RETURN NEW; END;' LANGUAGE
'plpgsql';

CREATE TRIGGER autostamp BEFORE UPDATE ON <table-name> FOR EACH ROW

EXECUTE PROCEDURE update_modtime();

The problem with this is, if I do UPDATE <table-name> set modtime =

<existing-value> WHERE <condition> where <existing-value> is the current
value of modtime, modtime then takes the value of now(). But if I'm
explicitly setting it to its existing value, I don't want the trigger to do
this. Of course, I could modify my scripts and stuff so that, if I don't
want modtime to change, I don't try to change it. But I'm not the only
user - and I think the behaviour would be more pleasant for the different
users if modtime always updated to what was specified, if a user was
explicitly setting it.