Before this $builder, I want to select a database, what shall I do? I don't want to use raw SQL. Thanks!
$builder = $this->modelsManager->createBuilder()  
            ->columns($cols)  
            ->distinct(true)  
            ->from($ZUC)  
            ->leftJoin($ZU, "$ZU.user_id = $ZUC.user_id")  
            ->leftJoin($ZSC, "$ZUC.subclass_id = $ZSC.subclass_id")  
            ->leftJoin($ZC, "$ZC.class_id = $ZSC.class_id")  
            ->leftJoin($ZCH, "$ZCH.order_no = $ZUC.order_no")  
            ->where($conStr, $conArr)  
            ->orderBy($order);