Select Query

QueryResult *SQLExec::select(const hsql::SelectStatement *statement) {

    ColumnNames *cn = new ColumnNames();
    ColumnAttributes *cas = new ColumnAttributes();
    DbRelation& table = tables->get_table(statement->fromTable->name);

    EvalPlan *plan = new EvalPlan(table);

    if(statement->whereClause != nullptr)
    {
        plan = new EvalPlan(get_where_conjunction(statement->whereClause),plan);
    }

    exprnList* select_list = statement->selectList; //TYPEDEF defined at the top

    if(select_list->at(0)->type == hsql::kExprStar)
    {   //for SELECT * queries
        *cn = table.get_column_names();
        plan = new EvalPlan(EvalPlan::ProjectAll, plan); //ProjectAll
    }

    else{ //for SELECT specific cols
            for(auto const element : *select_list)
                cn->push_back(element->name);

            plan = new EvalPlan(cn, plan); //Project specific cols
    }

    EvalPlan *optimized = plan->optimize();
    ValueDicts *rows = optimized->evaluate();

    cas = table.get_column_attributes(*cn);

    std::string message = "successfully returned " + std::to_string(rows->size()) + " rows";

    return new QueryResult(cn,cas,rows,message);
}