Foreign key relationship with composite primary keys in SQL Server 2005

sql-server-2005 foreign-key-relationship composite-primary-key
Black Eagle picture Black Eagle · Oct 22, 2010 · Viewed 94.9k times · Source

I have two tables 

Table1(
  FileID,
  BundledFileID,
  Domain)

and 

Table2(
  FileID,
  FileType,
  FileName)

In Table2 FileID and FileType are the composite primary key. I want to create a foreign key relationship from Table1.FileID to Table2.

Is it possible to do this?

Answer

marc_s picture marc_s · Oct 22, 2010

Since Table2 has a composite primary key (FileID, FileType), then any reference to it must also include both columns.

ALTER TABLE dbo.Table1
  ADD CONSTRAINT FK_Table1_Table2
  FOREIGN KEY(FileID, FileType) REFERENCES Table2(FileID, FileType)

Unless you have a unique constraint/index on the Table2.FileID field (but if so: why isn't this the PK??), you cannot create a FK relationship to only parts of the PK on the target table - just can't do it.

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