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47 lines
1.6 KiB
C++
47 lines
1.6 KiB
C++
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#pragma once
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#include <DB/IO/WriteHelpers.h>
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#include <DB/AggregateFunctions/IAggregateFunction.h>
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namespace DB
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{
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/** Интерфейс для ноль-арных агрегатных функций. Это, например, агрегатная функция count.
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*/
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template <typename T, typename Derived>
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class INullaryAggregateFunction : public IAggregateFunctionHelper<T>
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{
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private:
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Derived & getDerived() { return static_cast<Derived &>(*this); }
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const Derived & getDerived() const { return static_cast<const Derived &>(*this); }
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public:
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/// Получить тип результата по типам аргументов. Если функция неприменима для данных аргументов - кинуть исключение.
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void setArguments(const DataTypes & arguments) override final
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{
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if (arguments.size() != 0)
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throw Exception("Passed " + toString(arguments.size()) + " arguments to nullary aggregate function " + this->getName(),
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ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
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}
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/// Добавить значение.
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void add(AggregateDataPtr place, const IColumn ** columns, size_t row_num) const override final
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{
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getDerived().addImpl(place);
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}
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static void addFree(const IAggregateFunction * that, AggregateDataPtr place, const IColumn ** columns, size_t row_num)
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{
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return static_cast<const Derived &>(*that).addImpl(place);
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}
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IAggregateFunction::AddFunc getAddressOfAddFunction() const override final { return &addFree; }
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/** Реализуйте это в классе-наследнике:
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* void addImpl(AggregateDataPtr place) const;
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*/
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};
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}
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