Re: Is it possible to get username information while writingtrigger?

On 05/07/2018 01:39 AM, a wrote:
> Thank you for your reply;
>
> Please allow me to ask few more questions:
>
> 1, Since I'm writing a C trigger function, is there any method for me to
> get some of the basic information like the follow:
>
>      (1) Total number of rows;
>      (2) Rows' names;
>      (3) Value of OLD and NEW;
>
> 2, Is there any possibility of passing the SQL statement it self into
> the trigger?
>
> 3, Is it possible for me to exam before statement trigger so that I
> would be able to loop it once and copying the update information to the
> rest of rows.

Transition table(s):

https://www.postgresql.org/docs/10/static/sql-createtrigger.html

This is new to version 10 and I have not actually used this feature yet,
so all I can do is point you at the docs.

>
> Thanks a lot!
>
>
> ------------------ Original ------------------
> *From: * "Laurenz Albe";<laurenz(dot)albe(at)cybertec(dot)at>;
> *Send time:* Monday, May 7, 2018 3:57 PM
> *To:* "a"<372660931(at)qq(dot)com>; "pgsql-general"<pgsql-general(at)postgresql(dot)org>;
> *Subject: * Re: Is it possible to get username information while
> writingtrigger?
>
> a wrote:
> > What I want is to add a log entry at the last column of each row,
> which will record the
> > history update, insert automatically when relative statement is
> processed.
> >
> > I have read the documentation on triggers, which helps a lot.
> However, I may have few
> > more extra requirement to complete my wishes:
> >
> > 1, I would like to get the username of who executed the statement;
> >
> > 2, I would like to get the column name that is being updated;
> >
> > If it is possible and how should I do it??
>
> You could use the "current_user" function to get the current user.
>
> Mind, however, that updates caused by a cascading update from a
> foreign key constraint will be executed as the owner of the table,
> so it would be better to use "session_user" to avoid surprises.
>
> You cannot get the column name, because PostgreSQL updates a whole row,
> not an individual column. The best you can do is to check which
> column values are different in OLD and NEW.
>
> Yours,
> Laurenz Albe
> --
> Cybertec | https://www.cybertec-postgresql.com

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com