Question

我想执行此SQL语句，但我不能100％确定它是否能正常工作。

MERGE [dbo].[Word] as target
USING [dbo].[AWL] as source
ON target.[WordId] = source.[col1]
WHEN MATCHED THEN 
    UPDATE SET [AWL570Sublist] = col2;

有没有办法可以启动事务，执行MERGE，检查它是否有效，然后从SQL查询窗口回滚或提交？

Answer 1

出现错误回滚：

Scanner inputMenuChoice = new Scanner(System.in);



private int getMenuItem()
{
    System.out.println("\nPlease select from the following");
    System.out.println(ENTER_CAR + ". Enter licence plate and hours stayed");
    System.out.println(DISPLAY_CARS + ". Display all licence plates, hours and fees");
    System.out.println(DISPLAY_STATISTICS + ". Display Statistics");
    System.out.println(SEARCH_CARS + ". Search for car");
    System.out.println(EXIT + ". Exit the application");
    System.out.print("Enter choice==> ");
    return inputMenuChoice.nextInt();
}


private void processCars()
{
    int choice = getMenuItem();
    while (choice != EXIT)
    {
        switch (choice)
        {
            case ENTER_CAR:
                enterCar();
                break;
            case DISPLAY_CARS:
                displayAllCars();
                break;
            case DISPLAY_STATISTICS:
                displayStatistics();
                break;
            case SEARCH_CARS:
                searchCar();
                break;
            default:
                System.out.println("ERROR choice not recognised");
        }
        choice = getMenuItem();
    }
}


private void enterCar()
{

            String licPlate="",hr="";
            int d=1,carMax,numHr;
            int i=0;
            Scanner sa=new Scanner(System.in);
                                                                                                //for(int i=0;i<a.length;i++)
            {
                licPlate=JOptionPane.showInputDialog(null, "Please enter the license plate of the car");
                while(licPlate.isEmpty())
                {
                    if(licPlate.isEmpty())
                    {
                        JOptionPane.showMessageDialog(null, "Error - Licence Plate cannot be blank");
                        licPlate=JOptionPane.showInputDialog(null, "Please enter the license plate of the car");
                    }
                }
                hr=JOptionPane.showInputDialog(null, "Enter the number of hour(s) car was parked (1-12)");
                numHr=Integer.parseInt(hr);
                while(numHr>12 || numHr<1)
                {
                    if(numHr>12 || numHr<1)
                    {
                        JOptionPane.showMessageDialog(null, "Error - Hours must be between 1 and 12", "Error", JOptionPane.ERROR_MESSAGE);
                        hr=JOptionPane.showInputDialog(null, "Enter the number of hour(s) car was parked (1-12)");
                    }
                }
                System.out.printf("Details for car %d entered\n",d);
                a[i]=new Car(licPlate,numHr);
                d++;
            }
        {System.out.println(a[i]);}
        i++;

}


private void displayAllCars()
{
}


private void displayStatistics()
{
}


private void searchCar()
{
}


public static void main(String [] args)
{
    CarPark app = new CarPark();

    app.processCars();
}
}

好article有解释。

Answer 2

   BEGIN TRY;
   BEGIN TRAN;

        MERGE [dbo].[Word] as target
        USING [dbo].[AWL] as source
        ON target.[WordId] = source.[col1]
        WHEN MATCHED THEN 
            UPDATE SET [AWL570Sublist] = col2;  

    IF @@ERROR = 0
  BEGIN
      COMMIT TRAN;
  END
  END TRY
  BEGIN CATCH
            SELECT @@ERROR AS ERROR, ERROR_MESSAGE() AS [Error Description]
  ROLLBACK TRAN;
  END CATCH

Answer 3

BEGIN TRANSACTION

MERGE [dbo].[Word] as target
USING [dbo].[AWL] as source
ON target.[WordId] = source.[col1]
WHEN MATCHED THEN 
    UPDATE SET [AWL570Sublist] = col2;

-- Other statements

ROLLBACK TRANSACTION

请注意，如果您的操作导致标识列递增，则回滚将不会在事务开始时将下一个标识值重置为它的值。

如何实现可以回滚的SQL更新？

3 个答案: