如何保存自动生成的主键标识的外键列在同一个表

Question

以下是表结构：

CREATE TABLE [User] (
     [Id] bigint identity(1,1) not null, 
     [FirstName] nvarchar(100) not null, 
     [LastName] nvarchar(100) not null, 
     [Title] nvarchar(5) null, 
     [UserName] nvarchar(100) not null, 
     [Password] nvarchar(100) not null,  
     [Inactive] bit null, 
     [Created] Datetime not null, 
     [Creator] bigint not null, 
     [Modified] DateTime null, 
     [Modifier] bigint null 
     CONSTRAINT [PK_User] PRIMARY KEY CLUSTERED 
     (
      [Id] Asc 
     ) 
    ); 

IF NOT EXISTS (SELECT * FROM sys.foreign_keys WHERE object_id = OBJECT_ID(N'[FK_User_Creator]') AND parent_object_id = OBJECT_ID(N'[User]')) 
    ALTER TABLE [User] ADD CONSTRAINT [FK_User_Creator] FOREIGN KEY([Creator]) REFERENCES [User]([Id]) 
GO 


INSERT INTO [User] (Creator) Values ([Id] ?) 

这是一个情况下表为空，第一个用户是要在表中添加。否则，我没有问题。

如何在插入语句的同时在创建者列中插入Id？

Answer 1

一种方法可能是使用序列而不是标识列。下面的脚本可以达到相同的目的：

CREATE SEQUENCE dbo.useridsequence 
    AS int 
    START WITH 1 
    INCREMENT BY 1 ; 
GO 

CREATE TABLE [User] (
     [Id] bigint DEFAULT (NEXT VALUE FOR dbo.useridsequence) , 
     [FirstName] nvarchar(100) not null, 
     [LastName] nvarchar(100) not null, 
     [Title] nvarchar(5) null, 
     [UserName] nvarchar(100) not null, 
     [Password] nvarchar(100) not null,  
     [Inactive] bit null, 
     [Created] Datetime not null, 
     [Creator] bigint DEFAULT NEXT VALUE FOR dbo.useridsequence , 
     [Modified] DateTime null, 
     [Modifier] bigint null 
     CONSTRAINT [PK_User] PRIMARY KEY CLUSTERED 
     (
      [Id] Asc 
     ) 
    ); 

IF NOT EXISTS (SELECT * FROM sys.foreign_keys WHERE object_id = OBJECT_ID(N'[FK_User_Creator]') AND parent_object_id = OBJECT_ID(N'[User]')) 
    ALTER TABLE [User] ADD CONSTRAINT [FK_User_Creator] FOREIGN KEY([Creator]) REFERENCES [User]([Id]) 
GO 


INSERT INTO [User] 
(
    -- Id -- this column value is auto-generated 
    FirstName, 
    LastName, 
    Title, 
    UserName, 
    [Password], 
    Inactive, 
    Created, 
    Creator, 
    Modified, 
    Modifier 
) 
VALUES 
(
    'Foo', 
    'Bar', 
    'Title', 
    'UserName ', 
    'Password', 
    0, 
    GETDATE(), 
    DEFAULT, 
    GETDATE(), 
    1 
) 

SELECT * FROM [User] AS u 

结果：

Answer 2

简短的回答是，你不能这样做。我建议你的模型首先在逻辑上是有缺陷的。您是否打算将[用户]中的所有实际数据库用户（例如，创建用户...用于登录...）定义为行？你需要考虑这一点 - 但典型的答案是否定的。如果答案是肯定的，那么你完全不需要创建者列，因为它是多余的。所有你需要的是创建的日期 - 你可能应该定义一个默认值。

但是，如果你想这样做，你需要分两步来完成（你需要使列可以为空）。您为“真实”数据列插入一行（或多行）值。然后使用为id生成的标识值更新这些相同的行。一个例子显示了不同的方式来做到这一点

use tempdb; 
set nocount on; 
CREATE TABLE dbo.[user] (
     [user_id] smallint identity(3,10) not null primary key, 
     [name] nvarchar(20) not null, 
     [active] bit not null default (1), 
     [created] Datetime not null default (current_timestamp), 
     [creator] smallint null 
    ); 
ALTER TABLE dbo.[user] ADD CONSTRAINT [fk_user] FOREIGN KEY(creator) REFERENCES dbo.[user](user_id); 
GO 
-- add first row 
insert dbo.[user] (name) values ('test'); 
update dbo.[user] set creator = SCOPE_IDENTITY() where user_id = SCOPE_IDENTITY() 

-- add two more rows 
declare @ids table (user_id smallint not null); 
insert dbo.[user] (name) output inserted.user_id into @ids 
values ('nerk'), ('pom'); 
update t1 set creator = t1.user_id 
from @ids as newrows inner join dbo.[user] as t1 on newrows.user_id = t1.user_id; 
select * from dbo.[user] order by user_id; 

-- mess things up a bit 
delete dbo.[user] where name = 'pom'; 

-- create an error, consume an identity value 
insert dbo.[user](name) values (null); 

-- add 2 morerows 
delete @ids; 
insert dbo.[user] (name) output inserted.user_id into @ids 
values ('nerk'), ('pom'); 
update t1 set creator = t1.user_id 
from @ids as newrows inner join dbo.[user] as t1 on newrows.user_id = t1.user_id; 

select * from dbo.[user] order by user_id; 
drop table dbo.[user]; 

而且我改变了身份规范，以演示一些开发人员意识到的东西。它并不总是被定义为（1,1），并且下一个插入的值可能由于多种原因跳转 - 例如错误和缓存/重新启动。最后，我认为你会后悔用一个保留字命名表，因为引用它将需要使用分隔符。减轻痛苦。