Question

我有一张包含多条记录的表格：

User_Name（例如'TOM'）
Question_ID（例如'q002'）
答案（例如'D'）

我想创建一个触发器，这样任何人都无法两次提交相同问题的答案。 必须只是一个触发器。

CREATE TRIGGER trigger_Check_Duplicates

ON submit_Answer

FOR INSERT
AS

IF SELECT???

PRINT 'duplicate'

raiserror('cant submit answer to same question twice')

ROLLBACK

End

Answer 1

Create trigger

CREATE TRIGGER dbo.uniqueUserQuestion 
ON dbo.submit_Answer
INSTEAD OF INSERT
AS
BEGIN
    SET NOCOUNT ON
    IF EXISTS 
    (
        SELECT 1 
        FROM dbo.submit_Answer T 
        INNER JOIN INSERTED I 
        ON T.user_name = I.user_name 
            AND T.question_id = I.question_id
    )
    BEGIN
        -- Do dupe handling here
        PRINT 'duplicate'
        raiserror('cant submit answer to same question twice')
        return
    END

    -- actually add it in
    INSERT INTO
        dbo.submit_Answer
    SELECT
        *
    FROM
        INSERTED I
END
GO

Answer 2

MySql不支持INSTEAD OF触发器，这是您在此处需要使用的内容。在SQL Server中，您将使用INSTEAD OF INSERT触发器，在插入发生之前触发，您可以在其中写入重复的检查。但是，如果您可以避免触发，为什么不使用Stored Routine并在插入之前检查副本？

当然，如果你真的，真的不能使用约束。

编辑：更新MSSQL的答案。

以下是right from MSDN示例：

CREATE TRIGGER IO_Trig_INS_Employee ON Employee INSTEAD OF INSERT AS BEGIN SET NOCOUNT ON -- Check for duplicate Person. If there is no duplicate, do an insert. IF (NOT EXISTS (SELECT P.SSN FROM Person P, inserted I WHERE P.SSN = I.SSN)) INSERT INTO Person SELECT SSN,Name,Address,Birthdate FROM inserted ELSE -- Log an attempt to insert duplicate Person row in PersonDuplicates table. INSERT INTO PersonDuplicates SELECT SSN,Name,Address,Birthdate,SUSER_SNAME(),GETDATE() FROM inserted -- Check for duplicate Employee. If no there is duplicate, do an INSERT. IF (NOT EXISTS (SELECT E.SSN FROM EmployeeTable E, inserted WHERE E.SSN = inserted.SSN)) INSERT INTO EmployeeTable SELECT EmployeeID,SSN, Department, Salary FROM inserted ELSE --If there is a duplicate, change to UPDATE so that there will not --be a duplicate key violation error. UPDATE EmployeeTable SET EmployeeID = I.EmployeeID, Department = I.Department, Salary = I.Salary FROM EmployeeTable E, inserted I WHERE E.SSN = I.SSN END

你显然需要修改/简化你的情况，但基本的背景就在那里。

sql触发器可以跨行停止重复

2 个答案: