Trigger to delete past records in postgresql - sql

Question

I want only to maintain present 1 month records log details. need to delete past record log details.I tried this code however could not work this,
create sequence userseq1;
CREATE TABLE users
( id integer NOT NULL DEFAULT nextval('userseq1'::regclass)
);
INSERT INTO users VALUES(126);
CREATE TABLE History
( userid integer
, createdate timestamp
);
CREATE OR REPLACE FUNCTION recordcreatetime() RETURNS trigger language plpgsql
AS $$
DECLARE
BEGIN
INSERT INTO History values(new.id,NOW() );
RETURN NEW;
END;
$$;
CREATE TRIGGER user_hist
BEFORE INSERT ON users
FOR EACH ROW
EXECUTE procedure recordcreatetime();
However it is working to insert values sequencing one by one adding.I want to delete the previous 1 month record Log details.I tried this below code and it is not working
CREATE OR REPLACE FUNCTION trf_keep_row_number_steady()
RETURNS TRIGGER AS
$body$
DECLARE
BEGIN
IF (SELECT count(createdate) FROM history) > rownum_limit
THEN
DELETE FROM history
WHERE createdate = (SELECT min(createdate) FROM history);
END IF;
END;
$body$
LANGUAGE plpgsql;
CREATE TRIGGER tr_keep_row_number_steady
AFTER INSERT ON history
FOR EACH ROW EXECUTE PROCEDURE trf_keep_row_number_steady();

Answer 1

I can see in your second code block, you have a trigger on history table and you are trying to DELETE FROM history in that same trigger.
Insert / Update / Delete on a table through a trigger on the same table is not allowed. Please think of some other alternative, e.g., running a separate DELETE statement for the required cleanup of rows before or after your main INSERT statement.