创建复合主键的外键答案

【问题标题】：Creating a foreign key to compound primary key创建复合主键的外键
【发布时间】：2017-08-20 12:26:26
【问题描述】：

我有两张桌子 - Educators 和 Faculties：

CREATE TABLE [dbo].[Educators]
(
    [UserId] [nvarchar](128) NOT NULL,
    [FacultyId] [smallint] NOT NULL,
    [InstitutionUserId] [nvarchar](128) NOT NULL,

    CONSTRAINT [PK_Educators] 
        PRIMARY KEY CLUSTERED ([UserId] ASC)
)

CREATE TABLE [dbo].[Faculties]
(
    [InstitutionUserId] [nvarchar](128) NOT NULL,
    [FacultyId] [smallint] NOT NULL,

    CONSTRAINT [PK_UserFaculties] 
        PRIMARY KEY CLUSTERED ([InstitutionUserId] ASC, [FacultyId] ASC)
)

表Faculties 有一个由两列（InstitutionUserId 和FacultyId）组成的复合主键。我在Educators 表中也有相同的列。我想用外键将这两个表链接在一起。

所以，这是我的查询：

ALTER TABLE [dbo].[Educators] WITH CHECK 
    ADD CONSTRAINT [FK_Educators_FacultyId_Faculties_FacultyId] 
    FOREIGN KEY ([FacultyId], [InstitutionUserId])
    REFERENCES [dbo].[Faculties] ([FacultyId], [InstitutionUserId])

但我收到此错误消息：

消息 1776，第 16 级，状态 0，第 7 行
引用表 'dbo.Faculties' 中没有与外键 'FK_Educators_FacultyId_Faculties_FacultyId' 中的引用列列表匹配的主键或候选键。

消息 1750，第 16 级，状态 1，第 7 行
无法创建约束或索引。查看以前的错误。

如何解决这个问题？

【问题讨论】：

标签： sql sql-server database tsql azure-sql-server

【解决方案1】：

您的表格及其约束看起来不错。我能看到的唯一问题是主键中列的顺序

CONSTRAINT [PK_UserFaculties] PRIMARY KEY CLUSTERED 
(
    [InstitutionUserId] ASC,
    [FacultyId] ASC
)

与您在外键约束中声明的顺序不同

ALTER TABLE [dbo].[Educators]  WITH CHECK ADD  CONSTRAINT [FK_Educators_FacultyId_Faculties_FacultyId] FOREIGN KEY([FacultyId], [InstitutionUserId])
REFERENCES [dbo].[Faculties] ([FacultyId], [InstitutionUserId])

尝试更改外键声明中列的顺序，如下所示：

ALTER TABLE [dbo].[Educators]  WITH CHECK ADD  CONSTRAINT [FK_Educators_FacultyId_Faculties_FacultyId] FOREIGN KEY([InstitutionUserId], [FacultyId])
REFERENCES [dbo].[Faculties] ([InstitutionUserId], [FacultyId])

【讨论】：

【解决方案2】：

键的顺序应与定义的顺序相同：

ALTER TABLE dbo.Educators
    ADD CONSTRAINT FK_Educators_FacultyId_Faculties_FacultyId
        FOREIGN KEY(InstitutionUserId, FacultyId)
            REFERENCES dbo.Faculties(InstitutionUserId, FacultyId);

【讨论】：