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113 lines
2.2 KiB
C++
113 lines
2.2 KiB
C++
#pragma once
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#include <DB/IO/WriteHelpers.h>
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#include <DB/IO/ReadHelpers.h>
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#include <DB/AggregateFunctions/IUnaryAggregateFunction.h>
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namespace DB
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{
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struct AggregateFunctionMinTraits
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{
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static bool better(const Field & lhs, const Field & rhs) { return lhs < rhs; }
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static String name() { return "min"; }
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};
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struct AggregateFunctionMaxTraits
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{
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static bool better(const Field & lhs, const Field & rhs) { return lhs > rhs; }
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static String name() { return "max"; }
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};
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/// Берёт минимальное (или максимальное) значение. Если таких много - то первое попавшееся из них.
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template <typename Traits>
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class AggregateFunctionsMinMax : public IUnaryAggregateFunction
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{
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private:
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bool got;
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Field value;
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DataTypePtr type;
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public:
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AggregateFunctionsMinMax() : got(false) {}
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String getName() const { return Traits::name(); }
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String getTypeID() const { return Traits::name(); }
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AggregateFunctionPlainPtr cloneEmpty() const
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{
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AggregateFunctionsMinMax * res = new AggregateFunctionsMinMax;
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res->type = type;
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return res;
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}
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DataTypePtr getReturnType() const
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{
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return type;
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}
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void setArgument(const DataTypePtr & argument)
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{
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type = argument;
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}
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void addOne(const Field & value_)
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{
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if (got)
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{
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if (Traits::better(value_, value))
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value = value_;
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}
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else
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{
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got = true;
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value = value_;
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}
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}
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void merge(const IAggregateFunction & rhs)
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{
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if (got)
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{
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Field value_ = static_cast<const AggregateFunctionsMinMax &>(rhs).value;
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if (Traits::better(value_, value))
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value = value_;
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}
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else
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value = static_cast<const AggregateFunctionsMinMax &>(rhs).value;
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}
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void serialize(WriteBuffer & buf) const
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{
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type->serializeBinary(value, buf);
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}
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void deserializeMerge(ReadBuffer & buf)
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{
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if (got)
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{
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Field value_;
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type->deserializeBinary(value_, buf);
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if (Traits::better(value_, value))
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value = value_;
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}
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else
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type->deserializeBinary(value, buf);
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}
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Field getResult() const
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{
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return value;
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}
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};
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typedef AggregateFunctionsMinMax<AggregateFunctionMinTraits> AggregateFunctionMin;
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typedef AggregateFunctionsMinMax<AggregateFunctionMaxTraits> AggregateFunctionMax;
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}
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