Zend_Db_Table subquery

Goran's answer is the best answer. But if you want a zend_db_table style query, this would be an alternative:

$sql = $table->select()
          ->setIntegrityCheck(false)
          ->from('entries', new Zend_Db_Expr('DISTINCT festival'))
          ->where('status = ?', 1)
          ->where('festival_id NOT IN (?)',new Zend_Db_Expr("SELECT m.entry_id FROM entries AS e, mail_log as m WHERE m.entry_id = e.festival_id"));

I am not sure that Zend_Db_Table is capable of handling subqueries.

Why do you need to use Zend_Db_Table?

You can execute the query directly using Zend_Db::query().

$db = Zend_Db_Table::getDefaultAdapter();
$db->query("SELECT DISTINCT e.festival_id FROM entries AS e, mail_log as m 
    WHERE e.status = 1 
    AND e.festival_id 
    NOT IN (SELECT m.entry_id FROM entries AS e, mail_log as m WHERE m.entry_id = e.festival_id)
");

In my case, this works:

$subselect = $db->select()
  ->from(array('u1' => 'users'), 'departmentId')
  ->joinInner(array('d' => 'demand'), 'u1.userId = d.adminId', null)
  ->where('d.demandId = ?', $demand->getId());

$select2 = $db->select()
  ->from(array('u' => 'users'))
  ->where('u.departmentId = ?', $subselect);

The result was this:

SELECT `u`.* FROM `users` AS `u` WHERE u.departmentId = (SELECT `u1`.`departmentId` FROM `users` AS `u1` INNER JOIN `demand` AS `d` ON u1.userId = d.adminId WHERE d.demandId = '1')

I also try you sql.This is my code.

$select = $db->select()
      ->from(array('e' => ' entries'), array('festival_id'))
      ->distinct(true)
      ->where('e.status =?', 1)
      ->where('e.festival_id NOT IN (SELECT m.entry_id FROM entries AS e, mail_log as m WHERE m.entry_id = e.festival_id)')
      ->setIntegrityCheck(false);

I think this code more readable and simple than others.