$command = Yii->createCommand($sql)
if ($one) $command->addCondition($cond1);
if ($two) $command->addCondition($cond2);
$result = $command->queryAll();

db.coll.find({});

curs = myColl.find();
if(cond1) {
   curs2 = curs.find({cond2})
}