add unique constraint sql code example

Example 1: sql server add unique constraint

-- Add a Unique constraint and deifine the constraint name
ALTER TABLE TableName
ADD	CONSTRAINT TableName_ColumnName_Unique UNIQUE (ColumnName)

Example 2: set column as unique in sql server

ALTER TABLE Persons
ADD UNIQUE (ID);

Example 3: unique constraint mssql

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