Re: event trigger should provide more details

Thanks. This is helpful. Below is the result when I add a column to
public.accounts.

obj.classid, -- 1259
obj.objid, -- 16409
obj.objsubid, -- 0
obj.command_tag, -- ALTER TABLE
obj.object_type, -- table
obj.schema_name, -- public
obj.object_identity, -- public.accounts
obj.in_extension; -- f

The info useful for me is command_tag, object_type, object_identity.
classid, objid is not useful since object_identity is more explicit.
objsubid is not useful because I don't need comment
<https://www.postgresql.org/message-id/Pine.LNX.4.33.0212091822050.15095-100000@leary.csoft.net>
information for schema change.

Besides table name, I still need:
* which columns are added and their types.
* which columns have type change, the old and new types.
* which columns are dropped.

Will command field provide this info? I don't have an example and decoding
it needs C code
<https://www.postgresql.org/message-id/20190712222343.GA26924%40alvherre.pgsql>
. If I cannot get such info from pg_event_trigger_ddl_commands, I may need
to maintain schema snapshots myself and diff the old and new snapshots upon
an alter table/view event. Which way should I go? Thanks a lot.

On Tue, May 30, 2023 at 2:42 PM Erik Wienhold <ewie(at)ewie(dot)name> wrote:

> > On 30/05/2023 22:23 CEST Lian Jiang <jiangok2006(at)gmail(dot)com> wrote:
> >
> > I plan to create an event trigger to detect schema change (e.g.
> add/remove
> > a column, change column type), and write it into a separate table (e.g.
> > EVENTS). Then a process periodically reads this table to send schema
> change
> > notification. However, the event trigger (
> https://www.postgresql.org/docs/current/plpgsql-trigger.html)
> > (43.10.2. Triggers on Events) does not provide me info such as which
> table
> > is altered, old and new schema. Am I missing something? Thanks very much
> for
> > any hints.
>
> You must use ddl_command_end event triggers[0] and call function
> pg_event_trigger_ddl_commands[1] to get info such as altered table and
> column.
>
> [0] https://www.postgresql.org/docs/current/event-trigger-definition.html
> [1] https://www.postgresql.org/docs/current/functions-event-triggers.html
>
> --
> Erik
>
>
>

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