title: Make a varchar(50) column unique
body: <p>I have a column (which represents an e-mail) in a SQL Server database with <code>varchar(50)</code> as data type and I would like to make it unique (do not allow the same two e-mail addresses). I cannot find a way to make such column unique in SQL Server Management Studio. </p>
  
  <p>How to do that?</p>