Foreign key relationship with composite primary ke

问题:

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?

回答1:

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.

回答2:

marc has already given a pretty good answer. If the rows in Table1 only ever relate to one type of File (e.g. FileType 'ABC'), then you can add FileType to Table1 as a computed column:

ALTER TABLE Table1 ADD FileType as 'ABC'

Which you can then use in the Foreign Key.