RE: Event Triggers unable to capture the DDL script executed

[<n.kobzarev@xxxxxxxxxxxxxxxx>]

>>-----Исходное сообщение-----
>>От: Laurenz Albe <laurenz.albe@xxxxxxxxxxx> 
>>Отправлено: 22 февраля 2023 г. 12:52
>>Кому: Neethu P <neeth_3@xxxxxxxxxxx>; pgsql-general <pgsql-general@xxxxxxxxxxxxxx>
>>Тема: Re: Event Triggers unable to capture the DDL script executed

>>On Wed, 2023-02-22 at 07:57 +0000, Neethu P wrote:
>>> We are using event triggers to capture the DDL changes in a postgres database.
>>> However, we are unable to get the column information & the actual DDL 
>>> script executed, while a table is altered.
>>> Also, in the postgres documentation for pg_event_trigger_ddl_commands ()- it is mentioned as below.
>>> pg_ddl_command	A complete representation of the command, in internal
>>> format. Thiscannot be output directly, but it can be passed to other 
>>> functions to obtain different pieces of information about the command.
>>> 
>>> Is it possible to access pg_ddl_command in postgresql? Or is there any 
>>> scripts which can help to get theactual Alter DDL statement that was executed by the user?

>>That is simple if you write the event trigger in C.  I would say that that is the only way to get at the actual statement.

>>Yours,
>>Laurenz Albe



In MSSQL there is a brilliant possibility to have a server wide trigger to monitor commands. We are using It to have a history for all DDL operations.

Please try this (on new empty database) and give a feedback.

CREATE OR REPLACE FUNCTION public.notice_ddl()
    RETURNS event_trigger
    LANGUAGE 'plpgsql'
    COST 100
    VOLATILE NOT LEAKPROOF
AS $BODY$
DECLARE
    r RECORD;
begin
    raise info '%', session_user || ' ran '||tg_tag||' '||current_query();
    FOR r IN SELECT * FROM pg_event_trigger_ddl_commands() LOOP
        RAISE NOTICE 'we got a % event for object " %"', 
            r.command_tag, r.object_identity;
    END LOOP;
end;
$BODY$;

CREATE OR REPLACE FUNCTION public.notice_ddl_drop()
    RETURNS event_trigger
    LANGUAGE 'plpgsql'
    COST 100
    VOLATILE NOT LEAKPROOF
AS $BODY$
DECLARE
    r RECORD;
begin
    raise info '%', session_user || ' ran '||tg_tag||' '||current_query();
    FOR r IN SELECT * FROM pg_event_trigger_dropped_objects()
    LOOP
        RAISE NOTICE 'dropped: type "%" identity %',
                r.object_type, r.object_identity;
    END LOOP;
end;
$BODY$;


CREATE EVENT TRIGGER etg ON DDL_COMMAND_END
    EXECUTE PROCEDURE public.notice_ddl();

CREATE EVENT TRIGGER etg_drop ON SQL_DROP
    EXECUTE PROCEDURE public.notice_ddl_drop();