ClickHouse/dbms/src/AggregateFunctions/AggregateFunctionAvg.h

#pragma once

#include <IO/WriteHelpers.h>
#include <IO/ReadHelpers.h>

#include <DataTypes/DataTypesNumber.h>
#include <Columns/ColumnsNumber.h>

#include <AggregateFunctions/IAggregateFunction.h>


namespace DB
{


template <typename T>
struct AggregateFunctionAvgData
{
    T sum = 0;
    UInt64 count = 0;
};


/// Calculates arithmetic mean of numbers.
template <typename T>
class AggregateFunctionAvg final : public IAggregateFunctionDataHelper<AggregateFunctionAvgData<typename NearestFieldType<T>::Type>, AggregateFunctionAvg<T>>
{
public:
    String getName() const override { return "avg"; }

    DataTypePtr getReturnType() const override
    {
        return std::make_shared<DataTypeFloat64>();
    }

    void add(AggregateDataPtr place, const IColumn ** columns, size_t row_num, Arena *) const override
    {
        this->data(place).sum += static_cast<const ColumnVector<T> &>(*columns[0]).getData()[row_num];
        ++this->data(place).count;
    }

    void merge(AggregateDataPtr place, ConstAggregateDataPtr rhs, Arena *) const override
    {
        this->data(place).sum += this->data(rhs).sum;
        this->data(place).count += this->data(rhs).count;
    }

    void serialize(ConstAggregateDataPtr place, WriteBuffer & buf) const override
    {
        writeBinary(this->data(place).sum, buf);
        writeVarUInt(this->data(place).count, buf);
    }

    void deserialize(AggregateDataPtr place, ReadBuffer & buf, Arena *) const override
    {
        readBinary(this->data(place).sum, buf);
        readVarUInt(this->data(place).count, buf);
    }

    void insertResultInto(ConstAggregateDataPtr place, IColumn & to) const override
    {
        static_cast<ColumnFloat64 &>(to).getData().push_back(
            static_cast<Float64>(this->data(place).sum) / this->data(place).count);
    }

    const char * getHeaderFilePath() const override { return __FILE__; }
};


}