title: ISNULL function in SSIS
body: <p>I have a column <code>PhoneNumber varchar(50)</code> and i want to build an expression for a  derived column <code>PhoneNumberType varchar(50)</code> based on below,</p>
  
  <pre><code>IF PhoneNumber &lt;&gt; NULL then
  Set to ""Office""
  Else
  Set to NULL
  END IF
  </code></pre>
  
  <p>I tried as </p>
  
  <pre><code>!ISNULL(PhoneNumber ) ? "Office" : PhoneNumber 
  </code></pre>
  
  <p>But i am getting an error while mapping the column as </p>
  
  <blockquote>
    <p>Column PhoneNumberType  can not convert between unicode and
    non-unicode string data types</p>
  </blockquote>
  
  <p>Update : Can i just go to the advance editor of derived column component and select <code>string [DT_STR]</code> instead of auto generated , <code>unicode string [DT_WSTR]</code> data type in column properties ? </p>
  
  <p>is this a good practice ?</p>