Question

    CREATE TABLE [M].[SocialInfo]
    (
        [Id] UNIQUEIDENTIFIER NOT NULL PRIMARY KEY DEFAULT newid(), 
[MemberId] UNIQUEIDENTIFIER  DEFAULT newid(),
    [GroupId] UNIQUEIDENTIFIER  DEFAULT newid(),
        [NewsURL] VARCHAR(200) NULL,     
        CONSTRAINT [FK_SocialInfo_Member] FOREIGN KEY ([MemberId]) REFERENCES [M].[Member]([Id]), 
        CONSTRAINT [FK_SocialInfo_Group] FOREIGN KEY ([GroupId]) REFERENCES [M].[Group]([Id]) 
    )

如何使两个FK都可以为空？

我无法获得语法？

Answer 1

我认为你刚刚遗漏了专栏文章。

CREATE TABLE [M].[SocialInfo]
(
    [Id] UNIQUEIDENTIFIER NOT NULL PRIMARY KEY DEFAULT newid(), 
    [NewsURL] VARCHAR(200) NULL,     
    MemberId INT NULL,
    GroupId INT NULL,
    CONSTRAINT [FK_SocialInfo_Member] FOREIGN KEY ([MemberId]) REFERENCES [M].[Member]([Id]), 
    CONSTRAINT [FK_SocialInfo_Group] FOREIGN KEY ([GroupId]) REFERENCES [M].[Group]([Id]) 
)

Answer 2

外键的默认值没有意义 - 改为使用NULL

CREATE TABLE [M].[SocialInfo]
(
    [Id] UNIQUEIDENTIFIER NOT NULL PRIMARY KEY DEFAULT newid(), 
    [MemberId] UNIQUEIDENTIFIER  NULL,
    [GroupId] UNIQUEIDENTIFIER  NULL,
    [NewsURL] VARCHAR(200) NULL,     
    CONSTRAINT [FK_SocialInfo_Member] FOREIGN KEY ([MemberId]) REFERENCES [M].[Member]([Id]), 
    CONSTRAINT [FK_SocialInfo_Group] FOREIGN KEY ([GroupId]) REFERENCES [M].[Group]([Id]) 
)

Answer 3

我认为你需要把NULL关键字放在下面的链接中。

http://social.msdn.microsoft.com/Forums/sqlserver/en-US/325c11b9-e5c4-4db7-94e6-f82b44412b9b/is-it-possible-to-allow-null-values-in-foreign-key?forum=transactsql

此sqlfiddle也可能有用

http://sqlfiddle.com/#!3/39a0b/10

如何在SQL中将外键设为NULLABLE？

3 个答案: