How to impelment aggregation without group by projector ?

[Zhichao Liang]

Hi,

  I just wanna implement an aggregation on a specific column without group by projector, such as "SELECT SUM(attribute_name) FROM table_name", however, it's necessary for the API GroupAggregate to have a group by projector argument. Can anybody show me an example that impelments an aggregation without group by projector ? Thanks!

Best Regards!

Zhichao

[ptab]

Is ScalarAggregate (https://code.google.com/p/supersonic/source/browse/supersonic/cursor/core/aggregate.h#312) answer to your question ?

Piotr

[Zhichao Liang]

Yeah, ScalarAggregate is just what i need, thank you Piotr! In case some other guys encounter the same problem, i list an example of using ScalarAggregate as follows:

#include <iostream>

#include "supersonic/supersonic.h"

using std::cout;

using std::endl;

using supersonic::TupleSchema;

using supersonic::Attribute;

using supersonic::INT32;

using supersonic::NOT_NULLABLE;

using supersonic::View;

using supersonic::AggregationSpecification;

using supersonic::SUM;

using supersonic::Operation;

using supersonic::ScalarAggregate;

using supersonic::ScanView;

using supersonic::ResultView;

using supersonic::SucceedOrDie;

using supersonic::Cursor;

Cursor* SingleColumnSums(int32 *data, size_t row_number) {

        TupleSchema schema;

        schema.add_attribute(Attribute("data", INT32, NOT_NULLABLE));

        View input_view(schema);

        input_view.set_row_count(row_number);

        input_view.mutable_column(0)->Reset(data, NULL);

        scoped_ptr<AggregationSpecification> aggregator(new AggregationSpecification);

        aggregator->AddAggregation(SUM, "data", "data_sums");

        scoped_ptr<Operation> aggregation(ScalarAggregate(aggregator.release(), ScanView(input_view)));

        scoped_ptr<Cursor> bound_aggregation(SucceedOrDie(aggregation->CreateCursor()));

        return bound_aggregation.release();

}

int main(void) {

        const unsigned size = 8;

        int32 a[size] =  {  1,   2,   3,   1,   2,   3,   1,   2};

        scoped_ptr<Cursor> result_cursor(SingleColumnSums(a, size));

        ResultView result(result_cursor->Next(-1));

        if(!result.has_data()) {

                cout << "Failed to do the sum operation!" << endl;

                return -1;

        }

        View result_view(result.view());

        cout << "Result column number : " << result_view.column_count() << endl;

        cout << "Result row number : " << result_view.row_count() << endl;

        const int32* keys = result_view.column(0).typed_data<INT32>();

        cout << "Sum result : " << keys[0] << endl;

        return 0;

}

在 2013年4月12日星期五UTC+8下午7时41分35秒，ptab写道：