title: T-SQL NULLIF returns NULL for zero
body: <p>Why the script below returns <code>NULL</code> instead of <code>0</code>?</p>
  
  <pre><code>DECLARE @number BIGINT = 0;
  
  SELECT  NULLIF(@number, '');
  </code></pre>
  
  <p>According to the MSDN, it should return <code>0</code>:</p>
  
  <blockquote>
    <p><strong>NULLIF</strong><br>
    Returns a null value if the two specified expressions are equal.</p>
  </blockquote>
  
  <p>For SQL server, <code>0</code> and <code>''</code> is considered the same (=equal)? What is the logic behind?</p>