SET client_encoding TO 'LATIN1';

CREATE OR REPLACE FUNCTION before_insert() RETURNS trigger AS '
  DECLARE
   n integer;
  BEGIN
   IF tg_op = ''INSERT'' THEN
     select count(*) into n
      from files
      where date=new.date and url=new.url;
      IF n > 0 THEN
        RETURN NULL;
      ELSE
        RETURN new;
      END IF;
   END IF;
  END
' LANGUAGE plpgsql;

create table files
    (date TIMESTAMP,
     url VARCHAR(4000),
     type VARCHAR(100),
     status INTEGER,
     size INTEGER NOT NULL,
     arcname VARCHAR(100) NOT NULL,
     PRIMARY KEY (url,date));

CREATE TRIGGER before_insert_trigger BEFORE INSERT ON files
FOR EACH ROW EXECUTE PROCEDURE before_insert();