为什么此触发器未在postgres的表中插入记录？

Question

这是我的3张桌子。

Booking(Bookingid,date_of_booking,groupid,packageid,price)
Passenger(passengerid,groupid)
package(packageid,type)

这里是执行触发器时会调用的函数。

CREATE OR REPLACE FUNCTION COUNTPRICEFORTICKET3()
RETURNS TRIGGER AS 
$$
DECLARE
MYID INTEGER;
MYPRICE DOUBLE PRECISION;
BEGIN
SELECT COUNT(*) AS CNT INTO MYID FROM PASSENGER WHERE GROUPID=NEW.GROUPID 
GROUP BY GROUPID;
SELECT PRICE INTO MYPRICE FROM PACKAGE WHERE PACKAGEID=NEW.PACKAGEID;
NEW.PRICE:=MYPRICE * MYID;
RETURN NULL;
END;
$$
LANGUAGE plpgsql;


CREATE TRIGGER COUNTPRICE3 BEFORE INSERT ON BOOKING
FOR EACH ROW EXECUTE PROCEDURE COUNTPRICEFORTICKET3();

问题是触发器已成功执行，但是当我尝试使用INSERT查询将记录插入预订表时，它不会插入记录。

INSERT INTO BOOKING VALUES(NEXTVAL('BOOKSQ'),'26-SEP-2018',1201,700,NULL);