title: SQL Server NULL Integer to Empty String using ISNULL
body: <p>My curiosity always gets the best of me and I've searched online for an explanation to this and came up with nothing (could be because I didn't use the right terms.)</p>
  
  <p>Can someone please explain why SQL Server returns a value of zero (0) when the following is executed, instead of an empty string ('').</p>
  
  <pre><code>    DECLARE @I AS INT
      SET @I = NULL
      SELECT ISNULL(@I, '') -- 0
  </code></pre>