I needed CDbCriteria as a subquery so I did this in my ActiveRecord:
$subQuery=$this->commandBuilder->createFindCommand($this->tableName(),$criteria)->text;
$subQuery='('.str_replace(array_keys($criteria->params),array_values($criteria->params),$subQuery).') sq';
it works, but I think there may be a better and cleaner solution for this
any suggestion?