详解SQL Server 中的 ACID 属性

IF OBJECT_ID('dbo.Product','U') IS NOT NULL
    DROP TABLE dbo.Product
IF OBJECT_ID('dbo.ProductSales','U') IS NOT NULL
    DROP TABLE dbo.ProductSales
Go
CREATE TABLE Product
(
  ProductID INT PRIMARY KEY, 
  Name VARCHAR(40), 
  Price INT,
  Quantity INT
 )
GO
INSERT INTO Product VALUES(101, 'Laptop', 15000, 100)
INSERT INTO Product VALUES(102, 'Desktop', 20000, 150)
INSERT INTO Product VALUES(103, 'Mobile', 3000, 200)
INSERT INTO Product VALUES(104, 'Tablet', 4000, 250)
GO
CREATE TABLE ProductSales
(
  ProductSalesId INT PRIMARY KEY,
  ProductId INT,
  QuantitySold INT
) 
GO
INSERT INTO ProductSales VALUES(1, 101, 10)
INSERT INTO ProductSales VALUES(2, 102, 15)
INSERT INTO ProductSales VALUES(3, 103, 30)
INSERT INTO ProductSales VALUES(4, 104, 35)
GO

IF OBJECT_ID('spSellProduct','P') IS NOT NULL
    DROP PROCEDURE spSellProduct
GO
CREATE PROCEDURE spSellProduct
@ProductID INT,
@QuantityToSell INT
AS
BEGIN
  
  -- 首先我们需要检查待销售产品的可用库存
  DECLARE @StockAvailable INT
  SELECT @StockAvailable = Quantity FROM Product WHERE ProductId = @ProductId

  --如果可用库存小于要销售的数量,抛出错误
  IF(@StockAvailable < @QuantityToSell)
  BEGIN
    Raiserror('可用库存不足',16,1)
  END

  -- 如果可用库存充足
  ELSE
  BEGIN
    BEGIN TRY
      -- 我们需要开启一个事务
      BEGIN TRANSACTION

      -- 首先做减库存操作
      UPDATE Product SET Quantity = (Quantity - @QuantityToSell) WHERE ProductID = @ProductID

      -- 计算当前最大的产品销售ID,即 MaxProductSalesId
      DECLARE @MaxProductSalesId INT
      SELECT @MaxProductSalesId = CASE 
          WHEN MAX(ProductSalesId) IS NULL THEN 0 
          ELSE MAX(ProductSalesId) 
          END 
      FROM ProductSales

      -- 把 @MaxProductSalesId 加一, 所以我们会避免主键冲突 
      --(解释下,建表的时候,没有设置主键自增,所以需要人工处理自增)
      Set @MaxProductSalesId = @MaxProductSalesId + 1

      -- 把销售的产品数量记录到ProductSales表中
      INSERT INTO ProductSales VALUES (@MaxProductSalesId, @ProductId, @QuantityToSell)

      -- 最后,提交事务
      COMMIT TRANSACTION
    END TRY

    BEGIN CATCH
      -- 如果发生了异常,回滚事务
      ROLLBACK TRANSACTION
    END CATCH

  End
END

begin tran
update dbo.Product set Quantity = 150 where ProductID = 101
--rollback tran

select * from dbo.Product where ProductID = 101