ClickHouse/dbms/src/AggregateFunctions/AggregateFunctionIf.h

#pragma once

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


namespace DB
{

namespace ErrorCodes
{
    extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
}

/** Not an aggregate function, but an adapter of aggregate functions,
  * which any aggregate function `agg(x)` makes an aggregate function of the form `aggIf(x, cond)`.
  * The adapted aggregate function takes two arguments - a value and a condition,
  * and calculates the nested aggregate function for the values when the condition is satisfied.
  * For example, avgIf(x, cond) calculates the average x if `cond`.
  */
class AggregateFunctionIf final : public IAggregateFunctionHelper<AggregateFunctionIf>
{
private:
    AggregateFunctionPtr nested_func;
    size_t num_arguments;

public:
    AggregateFunctionIf(AggregateFunctionPtr nested, const DataTypes & types)
        : IAggregateFunctionHelper<AggregateFunctionIf>(types, nested->getParameters())
        , nested_func(nested), num_arguments(types.size())
    {
        if (num_arguments == 0)
            throw Exception("Aggregate function " + getName() + " require at least one argument", ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);

        if (!isUInt8(types.back()))
            throw Exception("Last argument for aggregate function " + getName() + " must be UInt8", ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
    }

    String getName() const override
    {
        return nested_func->getName() + "If";
    }

    DataTypePtr getReturnType() const override
    {
        return nested_func->getReturnType();
    }

    void create(AggregateDataPtr place) const override
    {
        nested_func->create(place);
    }

    void destroy(AggregateDataPtr place) const noexcept override
    {
        nested_func->destroy(place);
    }

    bool hasTrivialDestructor() const override
    {
        return nested_func->hasTrivialDestructor();
    }

    size_t sizeOfData() const override
    {
        return nested_func->sizeOfData();
    }

    size_t alignOfData() const override
    {
        return nested_func->alignOfData();
    }

    void add(AggregateDataPtr place, const IColumn ** columns, size_t row_num, Arena * arena) const override
    {
        if (static_cast<const ColumnUInt8 &>(*columns[num_arguments - 1]).getData()[row_num])
            nested_func->add(place, columns, row_num, arena);
    }

    void merge(AggregateDataPtr place, ConstAggregateDataPtr rhs, Arena * arena) const override
    {
        nested_func->merge(place, rhs, arena);
    }

    void serialize(ConstAggregateDataPtr place, WriteBuffer & buf) const override
    {
        nested_func->serialize(place, buf);
    }

    void deserialize(AggregateDataPtr place, ReadBuffer & buf, Arena * arena) const override
    {
        nested_func->deserialize(place, buf, arena);
    }

    void insertResultInto(ConstAggregateDataPtr place, IColumn & to) const override
    {
        nested_func->insertResultInto(place, to);
    }

    bool allocatesMemoryInArena() const override
    {
        return nested_func->allocatesMemoryInArena();
    }

    bool isState() const override
    {
        return nested_func->isState();
    }

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

}