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