函數錯誤 - postgresql

Question

我創建了這個函數，它檢查飛行的總成本是否已經被正確計算。它應該增加座位的價格，例如400乘以顧客要求的座位數目，例如2.如果客戶正確輸入總數，例如800，則應該成功返回查詢。如果他們沒有正確地輸入總數，例如1000那麼它應該引發異常'價格計算錯誤'。

CREATE FUNCTION check_totalcost() RETURNS trigger AS $check_totalcost$ 
    DECLARE seatprice int; 
    DECLARE noofseats int; 
    BEGIN 
     SELECT priceperseat INTO seatprice 
     FROM flight 
     WHERE flightid = flightid; 

     SELECT numseats INTO noofseats 
     FROM flightbooking 
     WHERE flightid = flightid; 

     IF(seatprice*noofseats != new.totalcost) THEN 
     RAISE EXCEPTION 'price has been calculated incorrectly'; 

     END IF; 
     RETURN NEW; 
    END; 
    $check_totalcost$ LANGUAGE plpgsql; 
    /* This is used to run the function above */ 
    CREATE TRIGGER insert_totalcost 
    BEFORE INSERT OR UPDATE ON flightbooking 
    FOR EACH ROW EXECUTE PROCEDURE check_totalcost(); 

當我輸入了不正確的總額，它引發異常這就是我想要的，但是當我輸入了正確的總量，這也引發了時，它應該成功返回查詢的除外。

Answer 1

查詢

SELECT priceperseat INTO seatprice 
FROM flight 
WHERE flightid = flightid; 

SELECT numseats INTO noofseats 
FROM flightbooking 
WHERE flightid = flightid; 

沒有多大意義，因爲條件總是爲真。 我想你想從插入/更新的記錄中獲得flightid。使用特殊的記錄NEW：

WHERE flightid = NEW.flightid; 

---

您的功能多了一個邏輯錯誤。座位數量也應該從new記錄中獲得。

CREATE OR REPLACE FUNCTION check_totalcost() 
RETURNS trigger AS $check_totalcost$ 
    DECLARE seatprice int; 
    BEGIN 
     SELECT priceperseat INTO seatprice 
     FROM flight 
     WHERE flightid = new.flightid; 

     IF seatprice * new.numseats != new.totalcost THEN 
      RAISE EXCEPTION 'price has been calculated incorrectly'; 

     END IF; 
     RETURN NEW; 
    END; 
    $check_totalcost$ LANGUAGE plpgsql;