Re: Triggers using PL/pgSQL

Hello,

Thanks a lot Aaron for the very quick and simple example. I just checked it on 7.4.5 also and it worked. I'll be able to continue with my development using the syntax of that example.

Regards,
-Thusitha

Aaron Bono <postgresql(at)aranya(dot)com> wrote: On 7/30/06, Thusitha Kodikara <kthusi(at)yahoo(dot)com> wrote: Hello,

I am interested in developing some triggers to keep track of records that are changed (possibly the changes of one or more specific columns). In addition to keeping the new values, I also need to keep the old values (may be on a separate table).

Though I have done similar things in other RDBMs using SQL, I find doing this in Postgres, a little bit complicated - may be because it needs to be done through a separate procedural language and through a separate function. The Postgres documentation also didn't provide much help ( the examples in C). I was mainly looking for example showing how to refer 'OLD' and 'NEW' rows using PL/pgSQL.

Can someone please direct me to some such examples?

How about this:

CREATE TABLE my_table (
my_table_id BIGSERIAL NOT NULL,
my_value VARCHAR(100) NOT NULL,
CONSTRAINT my_table_pkey PRIMARY KEY (my_table_id)
);

CREATE TABLE my_table_history (
my_table_id BIGINT NOT NULL,
my_value VARCHAR(100) NOT NULL,
create_dt TIMESTAMP NOT NULL,
CONSTRAINT my_table_history_pkey PRIMARY KEY (my_table_id, create_dt)
);

CREATE OR REPLACE FUNCTION my_table_history_fn () RETURNS SETOF opaque AS
'
BEGIN
-- if a trigger insert or update operation occurs
IF TG_OP = ''INSERT'' OR TG_OP = ''UPDATE'' THEN
execute
''INSERT INTO my_table_history ( '' ||
'' my_table_id, '' ||
'' my_value, '' ||
'' create_dt '' ||
'') VALUES ( '' ||
'' '''''' || NEW.my_table_id || '''''', '' ||
'' '''''' || NEW.my_value || '''''', '' ||
'' now() '' ||
'');''
;
RETURN NEW;
END IF;
END;
'
LANGUAGE 'plpgsql' VOLATILE CALLED ON NULL INPUT SECURITY INVOKER;

CREATE TRIGGER my_table_history_tr BEFORE UPDATE OR INSERT
ON my_table FOR EACH ROW
EXECUTE PROCEDURE my_table_history_fn();

I tried it out and it works in version 8.1.

==================================================================
Aaron Bono
Aranya Software Technologies, Inc.
http://www.aranya.com
==================================================================