title: Set default value in select statement(not use UNION statement)
body: <p>I would like to have a SELECT statement that will return specified default values if no rows are returned from the database.  </p>
  
  <p>We can use UNION to get the desired result like this question: "<a href="https://stackoverflow.com/questions/285666/how-to-set-a-default-row-for-a-query-that-returns-no-rows">How to set a default row for a query that returns no rows?</a>", but this gives an extra result row.</p>
  
  <p>example: </p>
  
  <pre><code>SELECT a 
      from TBL_TEST 
  UNION 
  SELECT 0 
      FROM DUAL
  </code></pre>
  
  <p>Is there a better way, or a standard SQL way to do this that will be portable across multiple database engines?</p>