how to insert auto increment value for trigger in postgresql? - sql

Question

This is the trigger from plpgsql -
CREATE TABLE emp (
empname text NOT NULL,
salary integer
);
CREATE TABLE emp_audit(
operation char(1) NOT NULL,
stamp timestamp NOT NULL,
userid text NOT NULL,
empname text NOT NULL,
salary integer
);
CREATE OR REPLACE FUNCTION process_emp_audit() RETURNS TRIGGER AS $emp_audit$
BEGIN
--
-- Create a row in emp_audit to reflect the operation performed on emp,
-- make use of the special variable TG_OP to work out the operation.
--
IF (TG_OP = 'DELETE') THEN
INSERT INTO emp_audit SELECT 'D', now(), user, OLD.*;
RETURN OLD;
ELSIF (TG_OP = 'UPDATE') THEN
INSERT INTO emp_audit SELECT 'U', now(), user, NEW.*;
RETURN NEW;
ELSIF (TG_OP = 'INSERT') THEN
INSERT INTO emp_audit SELECT 'I', now(), user, NEW.*;
RETURN NEW;
END IF;
RETURN NULL; -- result is ignored since this is an AFTER trigger
END;
$emp_audit$ LANGUAGE plpgsql;
CREATE TRIGGER emp_audit
AFTER INSERT OR UPDATE OR DELETE ON emp
FOR EACH ROW EXECUTE PROCEDURE process_emp_audit();
Now I want to add one more column in the emp_audit table which is a primary key, say emp_audit_id-
so now what should come here in the above SELECT query so that it can take care of PRIMARY KEY emp_audit_id as well.

Answer 1

Since you do not want to write out the field list on the INSERT statements (other readers: see comments below), you need to use a regular integer as PRIMARY KEY and a manually created sequence.
First alter the emp_audit table definition:
ALTER TABLE emp_audit ADD COLUMN emp_audit_id integer PRIMARY KEY
Create a sequence:
CREATE SEQUENCE seq_empaudit_pk;
In the INSERT statements, add the next value from the sequence:
IF (TG_OP = 'DELETE') THEN
INSERT INTO emp_audit SELECT 'D', now(), user, OLD.*, nextval(seq_empaudit_pk);
RETURN OLD;
ELSIF (TG_OP = 'UPDATE') THEN
INSERT INTO emp_audit SELECT 'U', now(), user, NEW.*, nextval(seq_empaudit_pk);
RETURN NEW;
ELSIF (TG_OP = 'INSERT') THEN
INSERT INTO emp_audit SELECT 'I', now(), user, NEW.*, nextval(seq_empaudit_pk);
RETURN NEW;
END IF;
Make sure to verify the order of the fields after you alter the table and list the fields in the SELECT query in exactly that order.