Adam,

Thanks for the advice. I will apply the logic you suggested.



I have read your advice about how to post. Since I use an email client

to read the support group, I didn't realize the implications of replying to
someone

else's post, but I will make sure that I do it correctly in future.



Graeme Edwards



_____

From: firebird-support@yahoogroups.com
[mailto:firebird-support@yahoogroups.com] On Behalf Of Adam
Sent: Wednesday, 15 February 2006 12:36 PM
To: firebird-support@yahoogroups.com
Subject: [firebird-support] Re: The New command in triggers



Graeme,

Do not reply to a post that has nothing to do with your comments.

1. It stuffs up newsreaders that organise automatically based on
replies.

2. People will not notice your post if they do not read Geoff's post
about "Read only databases and procedure blobs"

Instead of Reply, either click Post (web interface) or compose a new
email (from email client).

> I am currently having trouble developing a before update trigger to

set a

> timestamp field in a record based
>
> on values in other fields.
>
> The question I need answered is
>
> What is stored in new.Field if no change has been made to Field?

NEW.FIELD = OLD.FIELD

> My logic seems to break down when I assume that new.Field=old.Field
> indicates that no change has been made to the
>
> Field, and the possibility of Null in either new.Field or Old.Field

seems to

> complicate it more.

Your logic breaks when you assume the statement (NULL = NULL) is
true. NULL is a state not a value You need to specifically check
whether the OLD and NEW context variables have the same NULL state if
that is of interest to you.

If you consider NULL = NULL for the purpose of comparison, then you
will need to check each field like this.

IF ((OLD.FIELD <> NEW.FIELD) OR
(OLD.FIELD IS NOT NULL AND NEW.FIELD IS NULL) OR
(OLD.FIELD IS NULL AND NEW.FIELD IS NOT NULL)) THEN .....


Adam






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