ClickHouse/dbms/src/AggregateFunctions/AggregateFunctionArgMinMax.h

#pragma once

#include <common/StringRef.h>
#include <DataTypes/IDataType.h>
#include <AggregateFunctions/IAggregateFunction.h>
#include <AggregateFunctions/AggregateFunctionMinMaxAny.h> // SingleValueDataString used in embedded compiler


namespace DB
{

namespace ErrorCodes
{
    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
}


/// For possible values for template parameters, see AggregateFunctionMinMaxAny.h
template <typename ResultData, typename ValueData>
struct AggregateFunctionArgMinMaxData
{
    using ResultData_t = ResultData;
    using ValueData_t = ValueData;

    ResultData result;  // the argument at which the minimum/maximum value is reached.
    ValueData value;    // value for which the minimum/maximum is calculated.
};

/// Returns the first arg value found for the minimum/maximum value. Example: argMax(arg, value).
template <typename Data>
class AggregateFunctionArgMinMax final : public IAggregateFunctionDataHelper<Data, AggregateFunctionArgMinMax<Data>>
{
private:
    DataTypePtr type_res;
    DataTypePtr type_val;

public:
    AggregateFunctionArgMinMax(const DataTypePtr & type_res, const DataTypePtr & type_val)
        : type_res(type_res), type_val(type_val)
    {
        if (!type_val->isComparable())
            throw Exception("Illegal type " + type_val->getName() + " of second argument of aggregate function " + getName()
                + " because the values of that data type are not comparable", ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
    }

    String getName() const override { return StringRef(Data::ValueData_t::name()) == StringRef("min") ? "argMin" : "argMax"; }

    DataTypePtr getReturnType() const override
    {
        return type_res;
    }

    void add(AggregateDataPtr place, const IColumn ** columns, size_t row_num, Arena *) const override
    {
        if (this->data(place).value.changeIfBetter(*columns[1], row_num))
            this->data(place).result.change(*columns[0], row_num);
    }

    void merge(AggregateDataPtr place, ConstAggregateDataPtr rhs, Arena *) const override
    {
        if (this->data(place).value.changeIfBetter(this->data(rhs).value))
            this->data(place).result.change(this->data(rhs).result);
    }

    void serialize(ConstAggregateDataPtr place, WriteBuffer & buf) const override
    {
        this->data(place).result.write(buf, *type_res);
        this->data(place).value.write(buf, *type_val);
    }

    void deserialize(AggregateDataPtr place, ReadBuffer & buf, Arena *) const override
    {
        this->data(place).result.read(buf, *type_res);
        this->data(place).value.read(buf, *type_val);
    }

    void insertResultInto(ConstAggregateDataPtr place, IColumn & to) const override
    {
        this->data(place).result.insertResultInto(to);
    }

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

}