title: SQL query to find the common data
body: <p>I have a table in SQL Server 2008 with columns <code>serial, ida, idb</code>, and <code>remark</code>.</p>
  
  <p>Example data :</p>
  
  <pre><code>serial   ida      idb      remark
  1        3        4        null
  2        3        6        null
  3        3        7        null
  4        2        3        null
  5        4        7        null
  6        4        6        null
  </code></pre>
  
  <p>I want to select the common <code>idb</code> from <code>ida</code> 3 and 4. I am confused here how to write the SQL query for this. </p>
  
  <p>A little help will be appreciated.</p>