yii 常用的多表查询

         return $this->model()->getDbConnection()->createCommand()
                    ->select("t.type,t.title,t.class_id,t.thumb,t.hours,t.real_price,t.price,c.name,p.cert_id")
                    ->leftjoin(ClassroomClass::model()->tableName() .' c'," t.class_id = c.id")
                    ->leftjoin(ClassroomProductCert::model()->tableName() .' p'," t.id = p.product_id")
                    ->from($this->tableName() .' t')
                    ->where("t.id = $course_id")
                    ->queryRow();

第二种：

    $criteria =newCDbCriteria; 

    $criteria->addCondition("id=1"); //查询条件，即where id =1
    $criteria->addInCondition('id', array(1,2,3,4,5));//代表where id IN (1,23,,4,5,);
    $criteria->addNotInCondition('id',array(1,2,3,4,5));//与上面正好相法，是NOT IN
    $criteria->addCondition('id=1','OR');//这是OR条件，多个条件的时候，该条件是OR而非AND
    $criteria->addSearchCondition('name','分类');//搜索条件，其实代表了。。where name like '%分类%'
    $criteria->addBetweenCondition('id', 1, 4);//between1 and 4   

    $criteria->compare('id',1);   //这个方法比较特殊，他会根据你的参数自动处理成addCondition或者addInCondition，
                                    //即如果第二个参数是数组就会调用addInCondition  

    $criteria->addCondition("id = :id");
    $criteria->params[':id']=1;  

    $criteria->select = 'id,parentid,name';//代表了要查询的字段，默认select='*';
    $criteria->join = 'xxx'; //连接表
    $criteria->with = 'xxx';//调用relations
    $criteria->limit =10;   //取1条数据，如果小于0，则不作处理
    $criteria->offset =1;   //两条合并起来，则表示 limit 10 offset1,或者代表了。limit 1,10
    $criteria->order = 'xxx DESC,XXX ASC' ;//排序条件
    $criteria->group = 'group 条件';
    $criteria->having = 'having 条件 ';
    $criteria->distinct = FALSE;//是否唯一查询