Re: Triggers using PL/pgSQL - Mailing list pgsql-sql

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.