SQL Server：引用表中没有与外键'FK'中的引用列列表匹配的主键或候选键

Question

I've been trying to solve this error for several minutes but I don't know what am I missing from table definition.

The code for the tables are below:

Table Autocare :

CREATE TABLE [dbo].[Autocare] 
(
     [IDAutocar]    NUMERIC (18, 0) NOT NULL,
     [IDTipAutocar] NUMERIC (18, 0) NOT NULL,

     PRIMARY KEY CLUSTERED ([IDAutocar] ASC, [IDTipAutocar] ASC),

     CONSTRAINT [FK_Autogari_TipAutocar] 
        FOREIGN KEY ([IDTipAutocar]) 
        REFERENCES [dbo].[TipAutocar] ([IDTipAutocar])
);

Table Curse :

CREATE TABLE [dbo].[Curse]
(
    [IDCursa] NUMERIC (18, 0) NOT NULL PRIMARY KEY,
    [IDTraseu] NUMERIC (18, 0) NOT NULL, 
    [Data] TIMESTAMP NOT NULL, 
    [IDCompanie] NUMERIC (18, 0) NOT NULL, 
    [NrLocuri] NUMERIC (18, 0) NOT NULL, 
    [IDAutocar] NUMERIC (18, 0) NOT NULL, 

    CONSTRAINT [FK_Curse_Trasee] 
       FOREIGN KEY ([IDTraseu]) 
       REFERENCES [Trasee]([IDTraseu]), 
    CONSTRAINT [FK_Curse_Companii] 
       FOREIGN KEY ([IDCompanie]) 
       REFERENCES [Companii]([IDCompanie]), 
    CONSTRAINT [FK_Curse_Autocare] 
       FOREIGN KEY ([IDAutocar]) 
       REFERENCES [Autocare]([IDAutocar])
)

When I try to execute the second script I get the following error (and I know is something related to the relationship between tables) and I don't figure out where the problem might be. I'm a newbie into C# and SQL Server, so please forgive if I asked a stupid question.

Msg 1776, Level 16, State 0, Line 1
There are no primary or candidate keys in the referenced table 'Autocare' that match the referencing column list in the foreign key 'FK_Curse_Autocare'.

Msg 1750, Level 16, State 0, Line 1
Could not create constraint. See previous errors.

Answer 1

Your table Autocare has a compound primary key made up from two columns :

PRIMARY KEY CLUSTERED ([IDAutocar] ASC, [IDTipAutocar] ASC),

Therefore, any table that wishes to reference Autocare must also provide both columns in their foreign key!

So this will obviously not work:

CONSTRAINT [FK_Curse_Autocare] 
   FOREIGN KEY ([IDAutocar]) 
   REFERENCES [Autocare]([IDAutocar])

since it references only one of the two columns of the primary key of Autocare .

You need to add that second column IDTipAutocar to your Curse table and include it in your foreign key:

CONSTRAINT [FK_Curse_Autocare] 
   FOREIGN KEY ([IDAutocar], [IDTipAutocar]) 
   REFERENCES [Autocare]([IDAutocar], [IDTipAutocar])

Your foreign keys must always reference the WHOLE primary key - not just parts of it.

Answer 2

A foreign key must reference a unique key, be it primary or not. In your current supplied DDL, the unique identifier (primary key) in Autocare is the combination of IDAutocar and IDTipAutocar . On the other hand, you have Curse referencing Autocare.IDAutocar , which is not unique.

You can either add IDTipAutocar to Curse (and its foreign key definition):

CREATE TABLE [dbo].[Curse] (
    [IDCursa] NUMERIC (18, 0) NOT NULL PRIMARY KEY,
    [IDTraseu] NUMERIC (18, 0) NOT NULL, 
    [Data] TIMESTAMP NOT NULL, 
    [IDCompanie] NUMERIC (18, 0) NOT NULL, 
    [NrLocuri] NUMERIC (18, 0) NOT NULL, 
    [IDAutocar] NUMERIC (18, 0) NOT NULL, 
    [IDTipAutocar] NUMERIC (18, 0) NOT NULL,

    CONSTRAINT [FK_Curse_Trasee] 
        FOREIGN KEY ([IDTraseu]) 
        REFERENCES [Trasee]([IDTraseu]), 
    CONSTRAINT [FK_Curse_Companii]
        FOREIGN KEY ([IDCompanie])
        REFERENCES [Companii]([IDCompanie]), 
    CONSTRAINT [FK_Curse_Autocare]
        FOREIGN KEY ([IDAutocar], [IDTipAutocar]) 
        REFERENCES [Autocare]([IDAutocar], [IDTipAutocar])
)

Alternatively, you could remove IDTipAutocar from Autocare 's primary key definition:

CREATE TABLE [dbo].[Autocare] 
(
     [IDAutocar]    NUMERIC (18, 0) NOT NULL,
     [IDTipAutocar] NUMERIC (18, 0) NOT NULL,

     PRIMARY KEY CLUSTERED ([IDAutocar] ASC),

     CONSTRAINT [FK_Autogari_TipAutocar] 
        FOREIGN KEY ([IDTipAutocar]) 
        REFERENCES [dbo].[TipAutocar] ([IDTipAutocar])
);

Which ever makes more sense from your business logic's perspective.