title: Select statement with in ISNULL
body: <p>I am writing a stored procedure and within this procedure I am using isNULL. If the value is null I want to use a select statement as the replacement value is this even possible?</p>
  
  <pre><code>IF ISNULL(@v_FilePrefix, (SELECT @v_FilePrefix = TransactionTypePrefix 
                              FROM [ConfigTransactionType] 
                             WHERE TransactionTypeID = @TransactionTypeID));
  </code></pre>