Re: Detecting changes to certain fields in 'before update' trigger functions

Quoth "Richard Broersma" <richard.broersma@gmail.com>:
> On Mon, Dec 1, 2008 at 8:35 AM, Sebastian Tennant
> <sebyte@smolny.plus.com> wrote:
>>>>  IF (NEW.<column-name> != OLD.<column-name>) THEN ...
>>>
>>> IF( NEW.* IS DISTINCT FROM OLD.* ) THEN ...
>>>
>> I sometimes think this kind of gotcha is purposely buried, or not
>> addressed at all, in order to force users to read the manual.
>
> I wouldn't say it is intentionally buried.  I would say that the
> PostgreSQL manual focuses primarily is on "What are the PG features".
> While the manual may at times document some of the good/best practices
> to use by combining various PG features, I wouldn't say that its
> intention isn't to be an authoritative source on "How to use PG
> features."
>
> On the other hand, there are many ANSI-SQL books that focus on good
> practices.   For example, the need for the "IS DISTINCT FROM" when
> dealing with nulls would be discussed in an SQL book.  Once you have
> the theory down, you can turn to the PostgreSQL manual to find out how
> PostgreSQL implements this functionality.

That's sound advice and I take your point about the manual focussing on
Postgre features rather than SQL per se.  I have read one or two SQL
books but I'm very much a learn by doing person... and the fact is, I
haven't done much doing, until now.

May I wriggle out a little by saying that I didn't really mean what I
said, or rather, I failed to say what I really meant; that it sometimes
feels as if a gotcha has been buried in order to make you read the
manual.

Sebastian