Answers for "unique key on multiple columns in sql server"

add unique constraint sql server multiple columns

ALTER TABLE dbo.User
  ADD CONSTRAINT ucCodes UNIQUE (fcode, scode, dcode)

unique constraint mssql

USE AdventureWorks2012;  
GO  
CREATE TABLE Production.TransactionHistoryArchive4  
 (  
   TransactionID int NOT NULL,   
   CONSTRAINT AK_TransactionID UNIQUE(TransactionID)   
);   
GO