It took me quite some time but here is how to execute a MySQL stored procedure.

$connection = Propel::getConnection();
 
$query = 'CALL Proc(%s, %s, %s)';    
$query = sprintf($query, $var1, $var2, $var3);
 
$mysqli = $connection->getResource();
if($mysqli->multi_query($query)){
  do{
    if($result = $mysqli->use_result()){
      while($row = $result->fetch_assoc()){
        //
      }
      $result->free();
    }
  } while(($mysqli->next_result()));
}
 

Note that you should be using mysqli in order for this to work properly.

$sql = 'select * from ( select * from book order by weight desc limit 5 ) as T order by popularity';
$connection = Propel::getConnection();
$statement = $connection->createStatement(  );
$result = $statement->executeQuery( $sql , ResultSet::FETCHMODE_NUM);
return BookPeer::populateObjects( $result );

complement complex SQL in SYMFONY:

Example 1: SQL to be implemented:

SELECT b.id FROM article_mark a RIGHT JOIN article b ON a.article_id = b.id ORDER BY a.mark DESC,b.CREATED_AT DESC

Symfony implementation:

    $c=new Criteria();
    $c->addAlias('a', 'article_mark');              //!!!if not using alias of table, the generated sql is not correct
    $c->addAlias('b', 'article');
    $c->addSelectColumn('b.id');
    $c->addSelectColumn('a.article_id');            //!!!if one table has no column added, there's no table name after FROM clause;; actually this column is not what I need
    $c->addDescendingOrderByColumn('a.mark');
    $c->addDescendingOrderByColumn('b.CREATED_AT');
    $c->addJoin('a.ARTICLE_ID','b.ID','RIGHT JOIN');
    $art_marks=ArticlePeer::doSelectRS($c);         //!!! doSelect or doSelectOne can't be used

By this way, $art_marks is a MySQL recordset, using $art_marks[0] get value of column b.id;

Example 2: SQL to be implemented:

select SUM(score) from bury group by article_id having article_id=@ARTICLE_ID

Symfony implementation:

        $c=new Criteria();
        $c->addSelectColumn('SUM(score) as A');     //actually 'as A' has no use
        $c->addSelectColumn(BuryPeer::SCORE);              //!! without this, no table name in generated sql; actually this column is not what I need
 
        $c->addGroupByColumn('article_id');
        $crit=$c->getNewCriterion(BuryPeer::ARTICLE_ID,$article->getId());
        $c->addHaving($crit);
        $buries=BuryPeer::doSelectRS($c);       //only MySQL recordset can be used