如何使用触发器同时增加和同步两个表的主键？

Question

我有两个独立的数据库表来存储公司员工的个人和地址信息，如下所示：

CREATE TABLE [dbo].[Person]
(
    [BusinessEntityID] [int] IDENTITY(1,1) NOT NULL,
    [NationalIDNumber] [int] NULL,
    [FirstName] [nvarchar](50) NULL,
    [LastName] [nvarchar](50) NULL,

    CONSTRAINT [PK_Student] 
         PRIMARY KEY CLUSTERED ([BusinessEntityID] ASC)
                     WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, 
                           IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, 
                           ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
GO

CREATE TABLE [dbo].[Address]
(
    [AddressID] [int] NOT NULL,
    [AddressLine1] [varchar](150) NULL,
    [AddressLine2] [varchar](150) NULL,

    CONSTRAINT [PK_StudentAddress] 
        PRIMARY KEY CLUSTERED ([AddressID] ASC)
                    WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, 
                          IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, 
                          ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
GO

当我在[dbo].[Person] 中插入一个新行（如[FirstName]）时，它会自动创建一个[BusinessEntityID] 并一次递增一个。我想使用[BusinessEntityID] 值并将其插入[AddressID] 并为该员工的地址信息创建空间以便稍后输入。

可以使用触发器吗？我添加了这个触发器，但没有任何反应：

ALTER TRIGGER /*OR CREATE*/ [dbo].[auto_inc] 
ON [dbo].[Person]
AFTER INSERT
AS
BEGIN
    INSERT INTO Address(AddressID) SELECT p.BusinessEntityID FROM [Person] p
    UPDATE [Address]  SET AddressID = p.BusinessEntityID FROM [Person] p
END

Answer 1

如果您想捕获插入到Person 表中的标识值 - 您需要有一个AFTER INSERT 触发器，并且您需要查看触发器内的Inserted 伪表，以找出哪些行具有被插入。这些可以是多行 - 因此您需要相应地处理。

但是您真的想通过BusinessEntityId 向新创建的Person 添加一个“空”地址吗？这会产生大量空地址 - 有什么好处？另外：按照您现在的设置方式，一个人只能拥有一个地址——这也可能不是一个好主意。

所以如果你真的想要这样做 - 你需要一个类似这样的触发器：

CREATE OR ALTER TRIGGER [dbo].[auto_inc] 
ON [dbo].[Person]
AFTER INSERT
AS
BEGIN
    INSERT INTO dbo.Address (AddressID) 
        SELECT p.BusinessEntityID 
        FROM Inserted;
END

但是，从逻辑的角度来看，我认为这都是错误的。我会像这样设置Address 表：

CREATE TABLE dbo.Address
(
    -- use an IDENTITY for the unique ID for each address
    AddressID INT IDENTITY(1,1) NOT NULL,

    -- link the address to a person - this way, one person can have *multiple* addresses
    BusinessEntityID INT NOT NULL,
    AddressLine1 VARCHAR(150) NULL,
    AddressLine2 VARCHAR(150) NULL,
    -- more colums, like "AddressType" or something....

    CONSTRAINT PK_Address
        PRIMARY KEY CLUSTERED (AddressID ASC),
    -- establish foreign key constraint to Person
    CONSTRAINT FK_Address_Person
        FOREIGN KEY (BusinessEntityId) REFERENCES dbo.Person (BusinessEntityId)
)

我会不自动为您创建的每个人插入一个空地址 - 有什么用？？