Primary and Foreign Key at the same time

sql-server foreign-keys primary-key
Eduard Luca picture Eduard Luca · Jan 12, 2012 · Viewed 91.6k times · Source

Would it be possible in SQL Server 2008 to have a table created with 2 columns that are at the same time primary and foreign keys? If yes, how would such a code look like? I've searched and came up with nothing.

Answer

Marnix van Valen picture Marnix van Valen · Jan 12, 2012

Sure, no problem:

CREATE TABLE dbo.[User]
(
  Id int NOT NULL IDENTITY PRIMARY KEY,
  Name nvarchar(1024) NOT NULL
);

CREATE TABLE [Group] 
(
  Id int NOT NULL IDENTITY PRIMARY KEY,
  Name nvarchar(1024) NOT NULL
);

CREATE TABLE [UserToGroup]
(
  UserId int NOT NULL,
  GroupId int NOT NULL,
  PRIMARY KEY CLUSTERED ( UserId, GroupId ),
  FOREIGN KEY ( UserId ) REFERENCES [User] ( Id ) ON UPDATE  NO ACTION  ON DELETE  CASCADE,
  FOREIGN KEY ( GroupId ) REFERENCES [Group] ( Id ) ON UPDATE  NO ACTION  ON DELETE  CASCADE
);

This is quite commonly used to model many-to-many relations.

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