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47 lines
1.5 KiB
C++
47 lines
1.5 KiB
C++
#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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/** Interface for aggregate functions taking zero number of arguments. For example, this is 'count' aggregate function.
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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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/// By default, checks that number of arguments is zero. You could override if you would like to allow to have ignored arguments.
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void setArguments(const DataTypes & arguments) override
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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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/// Accumulate a value.
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void add(AggregateDataPtr place, const IColumn ** columns, size_t row_num, Arena *) 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, Arena *)
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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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/** Implement the following in descendant class:
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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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