Polymorphism puzzle

Hi,
I have abstract base class with some kids deriving from it. I want its kids to be concrete classes But I don't want to implement the all methods of the class. I'm trying to find a trick to go around doing this and I'm running out of thought on this. below is illustrative code of what I want to do.

Thanks for your help

Code:

 class BaseDB {
        BaseDB();
        virtual ResultSet getResults()=0;
        virtual void setResults(std::string sql)=0;
        virtual void someMoreFunction()=0;

};


class FirstChild :public BaseDB {
        ResultSet getResults(){
                //do some stuffs
        }
        
        void setResults(std::string sql){
                //some more stuffs
        }
        
        //I don't want to implement someMoreFunction() in this class
}

class SecondChild :public BaseDB {
        ResultSet getResults(){
                //do some stuffs
        }
        
        void someMoreFunction(){
                //some more stuffs
        }
        
        //I don't want to implement setResults(std::string sql) in this class
}