sql oracle - 对来自不同表的 2 列的约束

Question

我设计了一个机票系统预订航班。我想添加一个约束，使您可以插入的票数少于飞机上的座位数。

假设我插入了一个带有 10 个座位的飞机的航班。我只能插入该特定航班的 10 张机票。否则，应该会出现错误消息。

我尝试使用航班号的计数功能来触发。

CREATE OR REPLACE TRIGGER trg_ticket_BRIU 
    BEFORE INSERT OR UPDATE ON Ticket 
    FOR EACH ROW 
DECLARE
    l_numberofseats flight.numberofseats%type;
BEGIN
    select numberofseats into l_numberofseats
    from flight
    where flightnumber=:new.flightnumber;

    IF :new.count(flightnumber) > l_numberofseats
    THEN
        raise_application_error(-2000, 'Not enough seats');
    END IF;
END;

但我收到此错误

Trigger TRG_TICKET_BRIU compiled

LINE/COL  ERROR
--------- -------------------------------------------------------------
8/5       PLS-00049: bad bind variable 'NEW.COUNT'
Errors: check compiler log

Answer 1

就个人而言，我会添加一个AIRCRAFT 和一个SEAT 表：

CREATE TABLE aircraft (
  id           NUMBER
               GENERATED ALWAYS AS IDENTITY
               CONSTRAINT aircraft__id__pk PRIMARY KEY,
  tail_number  VARCHAR2(6)
               NOT NULL
               CONSTRAINT aircraft__tn__u UNIQUE
               CONSTRAINT aircraft__tn_chk CHECK(
                 REGEXP_LIKE(
                   tail_number,
                   '[A-Z]\d{1,5}|[A-Z]\d{1,4}[A-Z]|[A-Z]\d{1,3}[A-Z]{2}'
                 )
               ),
  manufacturer VARCHAR2(20)
               NOT NULL,
  model        VARCHAR2(20)
               NOT NULL,
  airline_id   CONSTRAINT aircraft__aid__fk REFERENCES airline(airline_id)
               NOT NULL
);

CREATE TABLE seat (
  id           NUMBER
               GENERATED ALWAYS AS IDENTITY
               CONSTRAINT seat__id__pk PRIMARY KEY,
  aircraft_id  CONSTRAINT seat__aid__fk REFERENCES aircraft(id)
               NOT NULL,
  seat_row     VARCHAR2(3)
               NOT NULL,
  seat_column  NUMBER
               NOT NULL,
  CONSTRAINT seat__aid_r_c__u UNIQUE (aircraft_id, seat_row, seat_column)
);

那么您的flight 表将引用aircraft：

CREATE TABLE flight (
  id           NUMBER
               GENERATED ALWAYS AS IDENTITY
               CONSTRAINT flight__id__pk PRIMARY KEY,
  aircraft_id  CONSTRAINT flight__aid__fk REFERENCES aircraft(id)
               NOT NULL
  -- ...
);

而ticket 将引用flight 和seat：

CREATE TABLE ticket (
  id           NUMBER
               GENERATED ALWAYS AS IDENTITY
               CONSTRAINT ticket__id__pk PRIMARY KEY,
  flight_id    CONSTRAINT ticket__fid__fk REFERENCES flight(id)
               NOT NULL,
  seat_id      CONSTRAINT ticket__sid__fk REFERENCES seat(id)
               NOT NULL,
  -- ...
  CONSTRAINT ticket__fid_sid__u UNIQUE (flight_id, seat_id)
);

那么您永远不能出售 aircraft 上不存在的 seat 并且不需要计算最大门票数量并将其与座位进行比较（并且 seat 已添加属性，例如其位置可以显示在机票上的飞机）。

然后，您需要确保引用一致性，对于ticket，flight 和seat 在同一个aircraft 上；这可以通过触发器来完成：

CREATE TRIGGER ticket_check_seat_on_flight
  BEFORE INSERT OR UPDATE ON ticket
  FOR EACH ROW
DECLARE
  is_valid NUMBER(1);
BEGIN
  SELECT 1
  INTO   is_valid
  FROM   flight f
         INNER JOIN seat s
         ON (f.aircraft_id = s.aircraft_id)
  WHERE  f.id = :NEW.flight_id
  AND    s.id = :NEW.seat_id;
EXCEPTION
  WHEN NO_DATA_FOUND THEN
    RAISE_APPLICATION_ERROR(
      -20000,
      'Flight and seat are on different aircraft.'
    );
END;
/

db小提琴here

Answer 2

您可以使用AFTER STATEMENT 触发器：

CREATE TRIGGER ticket__check_number_of_seats
  AFTER INSERT OR UPDATE OR DELETE ON ticket
DECLARE
  is_invalid NUMBER(1,0);
BEGIN
  SELECT 1
  INTO   is_invalid
  FROM   flight f
         INNER JOIN (
           SELECT flight_id,
                  COUNT(*) AS tickets_sold
           FROM   ticket
           GROUP BY flight_id
         ) t
         ON f.id = t.flight_id
  WHERE  t.tickets_sold > f.number_of_seats;
  
  RAISE_APPLICATION_ERROR(
    -20000,
    'Too many tickets sold for flight.'
  );
EXCEPTION
  WHEN NO_DATA_FOUND THEN
    NULL;
END;
/

通过使用复合触发器将每一行的flight_id 值整理到一个集合中，然后在语句之后仅检查这些航班的票数，可以提高效率；但是，我将把这个扩展作为 OP 的练习。

db小提琴here

Answer 3

正如其他人指出的那样，没有 :new.count 列。这是因为 :new（和 :old）创建了一个伪行，其中包含与表定义完全相同的列。此外，您将得到一个Mutating 异常，因为您需要从tickets 计算flight_number。但是，由于那是导致他触发触发的表，因此您无法引用它。那么该怎么做：创建一个compound trigger，和一个支持类型（嵌套表）。在其中使用after row 部分来捕获已处理的航班号。然后在after statement 部分，您可以选择每个航班的票数。如果该计数> 0，则引发您的异常。 （见Demo）

create type flight_tickets_ntt
         is table of integer;

create or replace trigger trg_ticket_ciu
   for update or insert on tickets
       compound trigger
       
    l_flights  flight_tickets_ntt := flight_tickets_ntt(); 
    
    after each row is 
    begin 
        if :new.flight_number not member of l_flights then 
            l_flights.extend ;
            l_flights(l_flights.count) := :new.flight_number; 
        end if; 
    end after each row; 
    
    after statement is
        l_flight_cnt flight.flight_number%type;
    begin 
         select count(*)
           into l_flight_cnt
           from flight f 
          where f.number_of_seats < 
                ( select count(*)
                    from tickets t 
                   where t.flight_number in 
                         ( select * 
                             from table (l_flights)
                         ) 
                );  
       
          if l_flight_cnt > 0 then 
             raise_application_error(-20000, 'Not enough seats');
          end if; 
           
    end after statement; 
end trg_ticket_ciu; 

还有一个您需要处理的问题：如果更新更改了航班号或可能（缺失的列）航班数据会发生什么。