title: SQL Server not null column update with unique constraint
body: <p>I have an existing table with 2 columns say <code>[Employee_Id , Salary]</code> with a few records in it.</p>
  
  <p>I want to add a new column say Employee_Code which is</p>
  
  <p>1 <code>Not Null</code></p>
  
  <p>2 <code>Unique</code></p>
  
  <p>Since the table already has some rows in it and the column is not nullable, I have to add a default value to it.</p>
  
  <p>Since I am adding a unique constraint, adding a default value will not work.</p>
  
  <p>How do I add a not null column to an existing table, having unique constraint?</p>