title: How to constraint no empty strings on an NVARCHAR column
body: <p>I add a <code>NOT NULL</code> constraint on my <code>NVARCHAR</code> column so it couldn't allow any empty values. but unfortunately SQL Server deals with <code>NULL</code> and empty values as two separate values!</p>
  
  <p>So how do I make the server throw an exception when inserting nothing to the column?</p>
  
  <p>I'm thinking using the constraint <a href="http://www.w3schools.com/Sql/sql_check.asp" rel="noreferrer">CHECK</a> but I didn't find any samples when used with <code>NVARCHAR</code> columns!</p>