ClickHouse/dbms/include/DB/AggregateFunctions/AggregateFunctionCount.h

#pragma once

#include <DB/IO/VarInt.h>

#include <array>
#include <DB/DataTypes/DataTypesNumberFixed.h>
#include <DB/DataTypes/DataTypeNullable.h>
#include <DB/AggregateFunctions/INullaryAggregateFunction.h>
#include <DB/AggregateFunctions/IUnaryAggregateFunction.h>
#include <DB/Columns/ColumnNullable.h>


namespace DB
{

struct AggregateFunctionCountData
{
	UInt64 count = 0;
};


/// Simply count number of calls.
class AggregateFunctionCount final : public INullaryAggregateFunction<AggregateFunctionCountData, AggregateFunctionCount>
{
public:
	String getName() const override { return "count"; }

	void setArguments(const DataTypes & arguments) override
	{
		/// You may pass some arguments. All of them are ignored.
	}

	DataTypePtr getReturnType() const override
	{
		return std::make_shared<DataTypeUInt64>();
	}

	void addImpl(AggregateDataPtr place) const
	{
		++data(place).count;
	}

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

	void serialize(ConstAggregateDataPtr place, WriteBuffer & buf) const override
	{
		writeVarUInt(data(place).count, buf);
	}

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

	void insertResultInto(ConstAggregateDataPtr place, IColumn & to) const override
	{
		static_cast<ColumnUInt64 &>(to).getData().push_back(data(place).count);
	}

	/// May be used for optimization.
	void addDelta(AggregateDataPtr place, UInt64 x) const
	{
		data(place).count += x;
	}
};


/// Simply count number of not-NULL values.
class AggregateFunctionCountNotNullUnary final : public IUnaryAggregateFunction<AggregateFunctionCountData, AggregateFunctionCountNotNullUnary>
{
public:
	String getName() const override { return "count"; }

	DataTypePtr getReturnType() const override
	{
		return std::make_shared<DataTypeUInt64>();
	}

	void addImpl(AggregateDataPtr place, const IColumn & column, size_t row_num, Arena * arena) const
	{
		data(place).count += !static_cast<const ColumnNullable &>(column).isNullAt(row_num);
	}

	void setArgument(const DataTypePtr & argument)
	{
		if (!argument->isNullable() && !argument->isNull())
			throw Exception("Not Nullable argument passed to aggregate function count", ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
	}

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

	void serialize(ConstAggregateDataPtr place, WriteBuffer & buf) const override
	{
		writeVarUInt(data(place).count, buf);
	}

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

	void insertResultInto(ConstAggregateDataPtr place, IColumn & to) const override
	{
		static_cast<ColumnUInt64 &>(to).getData().push_back(data(place).count);
	}
};


/// Count number of calls where all arguments are not NULL.
class AggregateFunctionCountNotNullVariadic final : public IAggregateFunctionHelper<AggregateFunctionCountData>
{
public:
	String getName() const override { return "count"; }

	DataTypePtr getReturnType() const override
	{
		return std::make_shared<DataTypeUInt64>();
	}

	void setArguments(const DataTypes & arguments) override
	{
		number_of_arguments = arguments.size();

		if (number_of_arguments == 1)
			throw Exception("Logical error: single argument is passed to AggregateFunctionCountNotNullVariadic", ErrorCodes::LOGICAL_ERROR);

		if (number_of_arguments > MAX_ARGS)
			throw Exception("Maximum number of arguments for aggregate function with Nullable types is " + toString(MAX_ARGS),
				ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);

		for (size_t i = 0; i < number_of_arguments; ++i)
			is_nullable[i] = arguments[i]->isNullable() || arguments[i]->isNull();
	}

	void add(AggregateDataPtr place, const IColumn ** columns, size_t row_num, Arena * arena) const override
	{
		for (size_t i = 0; i < number_of_arguments; ++i)
			if (is_nullable[i] && static_cast<const ColumnNullable &>(*columns[i]).isNullAt(row_num))
				return;

		++data(place).count;
	}

	static void addFree(const IAggregateFunction * that, AggregateDataPtr place,
		const IColumn ** columns, size_t row_num, Arena * arena)
	{
		return static_cast<const AggregateFunctionCountNotNullVariadic &>(*that).add(place, columns, row_num, arena);
	}

	AddFunc getAddressOfAddFunction() const override
	{
		return &addFree;
	}

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

	void serialize(ConstAggregateDataPtr place, WriteBuffer & buf) const override
	{
		writeVarUInt(data(place).count, buf);
	}

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

	void insertResultInto(ConstAggregateDataPtr place, IColumn & to) const override
	{
		static_cast<ColumnUInt64 &>(to).getData().push_back(data(place).count);
	}

private:
	enum { MAX_ARGS = 8 };
	size_t number_of_arguments = 0;
	std::array<char, MAX_ARGS> is_nullable;	/// Plain array is better than std::vector due to one indirection less.
};

}