防止基于用户定义函数的结果更新列的触发器

Question

我们有 DVD 出租公司。在此特定场景中，我们仅考虑会员、租赁和会员资格 tables.

任务是编写一个触发器，防止客户收到 DVD 如果他们使用该功能达到会员合同规定的每月 DVD 租赁限额。

我的触发器导致无限循环。它可以在没有 While 循环的情况下工作，但是如果我考虑对 Rental table 进行多次更新，它就无法正常工作。我哪里错了？

-- do not run, infinite loop
CREATE OR ALTER TRIGGER trg_Rental_StopDvdShip
ON RENTAL
FOR UPDATE
AS
BEGIN
    DECLARE @MemberId INT
    DECLARE @RentalId INT
    SELECT * INTO #TempTable FROM inserted
    WHILE (EXISTS (SELECT RentalId FROM #TempTable))
    BEGIN
        IF UPDATE(RentalShippedDate)
        BEGIN
            IF (SELECT TotalDvdLeft FROM dvd_numb_left(@MemberId)) <= 0
            BEGIN
                ROLLBACK
                RAISERROR ('YOU HAVE REACHED MONTHLY LIMIT FOR DVD RENTALS', 16, 1)
            END;
        END;
        DELETE FROM #TempTable WHERE RentalID = @RentalId
    END;
END;

我的函数如下所示：


CREATE OR ALTER FUNCTION dvd_numb_left(@member_id INT)
RETURNS @tab_dvd_numb_left TABLE(MemberId INT, Name VARCHAR(50), TotalDvdLeft INT, AtTimeDvdLeft INT)
AS
BEGIN
    DECLARE @name VARCHAR(50)
    DECLARE @dvd_total_left INT
    DECLARE @dvd_at_time_left INT
    DECLARE @dvd_limit INT
    DECLARE @dvd_rented INT
    DECLARE @dvd_at_time INT
    DECLARE @dvd_on_rent INT
    SET @dvd_limit = (SELECT Membership.MembershipLimitPerMonth FROM Membership
        WHERE Membership.MembershipId = (SELECT Member.MembershipId FROM Member WHERE Member.MemberId = @member_id))
    SET @dvd_rented = (SELECT COUNT(Rental.MemberId) FROM Rental
        WHERE CONCAT(month(Rental.RentalShippedDate), '.', year(Rental.RentalShippedDate)) = CONCAT(month(GETDATE()), '.', year(GETDATE())) AND Rental.MemberId = @member_id)
    SET @dvd_at_time = (SELECT Membership.DVDAtTime FROM Membership
        WHERE Membership.MembershipId = (SELECT Member.MembershipId FROM Member WHERE Member.MemberId = @member_id))
    SET @dvd_on_rent = (SELECT COUNT(Rental.MemberId) FROM Rental
        WHERE Rental.MemberId = @member_id AND Rental.RentalReturnedDate IS NULL)
    SET @name = (SELECT CONCAT(Member.MemberFirstName, ' ', Member.MemberLastName) FROM Member WHERE Member.MemberId = @member_id)
    SET @dvd_total_left = @dvd_limit - @dvd_rented
    SET @dvd_at_time_left = @dvd_at_time - @dvd_on_rent
    IF @dvd_total_left < 0
    BEGIN
        SET @dvd_total_left = 0
        SET @dvd_at_time_left = 0
        INSERT INTO @tab_dvd_numb_left(MemberId, Name, TotalDvdLeft, AtTimeDvdLeft)
        VALUES(@member_id, @name, @dvd_total_left, @dvd_at_time_left)
        RETURN;
    END
    INSERT INTO @tab_dvd_numb_left(MemberId, Name, TotalDvdLeft, AtTimeDvdLeft)
    VALUES(@member_id, @name, @dvd_total_left, @dvd_at_time_left)
    RETURN;
END;

很高兴收到任何建议。

Answer 1

您的主要问题是，即使您填充了 #TempTable，您也永远不会从中提取任何值。

CREATE OR ALTER TRIGGER trg_Rental_StopDvdShip
ON RENTAL
FOR UPDATE
AS
BEGIN
    DECLARE @MemberId INT, @RentalId INT;

    -- Move test for column update to the first test as it applies to the entire update, not per row.
    IF UPDATE(RentalShippedDate)
    BEGIN
        SELECT * INTO #TempTable FROM inserted;
        WHILE (EXISTS (SELECT RentalId FROM #TempTable))
        BEGIN
            -- Actually pull some information from #TempTable - this wasn't happening before
            SELECT TOP 1 @RentalID = RentalId, @MemberId = MemberId FROM  #TempTable;

            -- Select our values to its working
            -- SELECT @RentalID, @MemberId;

            IF (SELECT TotalDvdLeft FROM dvd_numb_left(@MemberId)) <= 0
            BEGIN
                ROLLBACK
                RAISERROR ('YOU HAVE REACHED MONTHLY LIMIT FOR DVD RENTALS', 16, 1)
            END;

            -- Delete the current handled row
            DELETE FROM #TempTable WHERE RentalID = @RentalId
        END;

        -- For neatness I always drop temp tables, makes testing easier also
        DROP TABLE #TempTable;
    END;
END;

调试像这样的简单触发器的一种简单方法是复制 T-SQL，然后创建一个 @Inserted table 变量，例如

DECLARE @Inserted table (RentalId INT, MemberId INT);

INSERT INTO @Inserted (RentalId, MemberId)
VALUES (1, 1),  (2, 2);

    DECLARE @MemberId INT, @RentalId INT;

    -- Move test for column update to the first test as it applies to the entire update, not per row.
    -- IF UPDATE(RentalShippedDate)
    BEGIN
        SELECT * INTO #TempTable FROM @inserted;
        WHILE (EXISTS (SELECT RentalId FROM #TempTable))
        BEGIN
            -- Actually pull some information from #TempTable - this wasn't happening before
            SELECT TOP 1 @RentalID = RentalId, @MemberId = MemberId FROM  #TempTable;

            -- Select our values to its working
            SELECT @RentalID, @MemberId;

            -- IF (SELECT TotalDvdLeft FROM dvd_numb_left(@MemberId)) <= 0
            -- BEGIN
            --     ROLLBACK
            --     RAISERROR ('YOU HAVE REACHED MONTHLY LIMIT FOR DVD RENTALS', 16, 1)
            -- END;

            -- Delete the current handled row
            DELETE FROM #TempTable WHERE RentalID = @RentalId
        END;

        -- For neatness I always drop temp tables, makes testing easier also
        DROP TABLE #TempTable;
    END;

注意：throw 是抛出错误的推荐方法，而不是 raiserror。

Answer 2

另一件需要考虑的事情是，由于一些副作用，您必须尝试将 UDF 转换为内联 TVF。

喜欢这个：

CREATE OR ALTER FUNCTION dvd_numb_left(@member_id INT)
RETURNS TABLE
AS
RETURN
(
WITH 
TM AS
(SELECT Membership.MembershipLimitPerMonth AS dvd_limit,
        Membership.DVDAtTime AS dvd_at_time,
        CONCAT(Member.MemberFirstName, ' ', Member.MemberLastName) AS [name]
 FROM   Membership AS MS
       JOIN Member AS M
             ON MS.MembershipId = M.MembershipId
 WHERE M.MemberId = @member_id
),
TR AS
(SELECT COUNT(Rental.MemberId) AS dvd_rented
 FROM   Rental
 WHERE  YEAR(Rental.RentalShippedDate ) = YEAR(GETDATE)
   AND  MONTH(Rental.RentalShippedDate ) = MONTH(GETDATE)
   AND  Rental.MemberId = @member_id
)
SELECT MemberId, [Name], 
       CASE WHEN dvd_limit - dvd_rented < 0 THEN 0 ELSE dvd_limit - dvd_rented END AS TotalDvdLeft,
       CASE WHEN dvd_limit - dvd_rented < 0  THEN 0 ELSE dvd_at_time - dvd_on_rent END AS AtTimeDvdLeft
FROM   TM CROSS JOIN TR
);
GO

哪个效率会高很多。

获得性能的绝对规则是：尽量保持在"SET BASED"代码中而不是迭代代码。

上述功能可以通过优化器进行优化，而您的功能不能而且将需要 4 次访问相同的表。

防止基于用户定义函数的结果更新列的触发器

Trigger that prevents update of column based on result of the user defined function

sql

sql-server

database-trigger