Date: Wed, 27 Apr 2022 13:46:05 +0200
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Jian He <hejian.mark@gmail.com>
Cc: pgsql-docs@lists.postgresql.org
Subject: Re: 43.10 Trigger Functions one sentences kind of not easy to
 understand.
Message-ID: <202204271146.waevseyzqnsb@alvherre.pgsql>
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On 2022-Apr-27, Jian He wrote:

> https://www.postgresql.org/docs/current/plpgsql-trigger.html
> 
> > *Returning a row value different from the original value
> > of NEW alters the row that will be inserted or updated.*

> I just want confirm the highlighted sentence  is equivalent as the
> following sql code:

Yes:

> begin;
> > CREATE TABLE documents (
> >     docdesc text,
> >     misc text,
> >     modification_time timestamp with time zone DEFAULT now()
> > );
> > CREATE FUNCTION documents_update_mod_time() RETURNS trigger
> > AS $$
> >     begin
> >     new.modification_time := now();
> >
>     return new;
> >
>     end
> > $$
> >     LANGUAGE plpgsql;
> > CREATE TRIGGER documents_modification_time
> >     BEFORE INSERT OR UPDATE ON documents
> >     FOR EACH ROW
> >     EXECUTE PROCEDURE documents_update_mod_time();
> > commit;

This is the usual way to modify the row being inserted.

> As a non-native english speaker, I kind of feel this sentence quite hard to
> understand....

Maybe you can split it up at periods and think about individual parts
separately.  The docs are intentionally packed very densely with
information, to avoid making them longer than they already are.

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/