postgresql错误：语法错误位于或接近；“返回”；

我对psql一无所知。当我使用 要做一些作业，系统会返回此错误

ERROR: syntax error at or near "RETURNS"

感谢您的帮助。 这是我的psql：

CREATE TABLE HotelStays
(roomNum INTEGER NOT NULL,
arrDate DATE NOT NULL,
depDate DATE NOT NULL,
guestName CHAR(30) NOT NULL,
PRIMARY KEY (roomNum, arrDate))
;

CREATE OR REPLACE FUNCTION stopInsert RETURNS trigger AS
$body$
DECLARE
  availableArrDate DATE;
  checkRoomNum INTEGER;
BEGIN
  if (NEW.arrDate >= NEW.depDate) then
    return null;
   end if;

  checkRoomNum = NEW.roomNum;

  select h.depDate into availableArrDate
  from HotelStays h
  where h.roomNum = checkRoomNum
  order by h.depDate DESC
  LIMIT 1;
  if (availableArrDate > NEW.arrDate)
    return null;
  end if;
END;
$body$ LANGUAGE plpgsql;

create trigger stopInsert before insert ON HotelStays 
For each row
execute procedure stopInsert();

---

函数名中需要有

（）

：

CREATE OR REPLACE FUNCTION stopInsert() RETURNS trigger AS
                                      ^
--------------------------------------|

如果

语句也不正确，则表示缺少

然后

if (availableArrDate > NEW.arrDate) then --<< THEN is required
  return null;
end if;

if（availableArrDate>NEW.arrDate）则--