PL/PgSQL creating a conditional trigger on insert

Question

I'm working on my first ever Trigger. When I'm doing an INSERT on table I want to conditionaly remove rows from other table.

Here is a trigger:

CREATE OR REPLACE FUNCTION clear_seen_by()
  RETURNS trigger AS
$BODY$
    BEGIN
         IF (OLD.popup = '1') THEN
              DELETE FROM news_seen_by;
            END IF;

        RETURN NULL;
    END;
   $BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;

Invoked by:

  CREATE TRIGGER clear_seen_by
  AFTER INSERT
  ON news
  FOR EACH STATEMENT
  EXECUTE PROCEDURE clear_seen_by();

As an error I see that NEW or OLD (if I motify the trigger) is not declared/unknown. Where is the problem?

Answer 1

In an INSERT statement you do not have an OLD record defined.

You should use NEW.popup instead, and also declare the trigger to be FOR EACH ROW.

  CREATE OR REPLACE FUNCTION clear_seen_by() RETURNS trigger AS
  $BODY$
    BEGIN
      IF (NEW.popup = '1') THEN
        DELETE FROM news_seen_by;
      END IF;

      RETURN NULL;
    END;
  $BODY$
  LANGUAGE plpgsql VOLATILE COST 100;


  CREATE TRIGGER
    clear_seen_by
  AFTER INSERT ON
    news
  FOR EACH ROW EXECUTE PROCEDURE
    clear_seen_by();

Answer 2

You declare a trigger FOR EACH STATEMENT. Maybe you need FOR EACH ROW?

FOR EACH STATEMENT triggers do not have NEW and OLD.