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

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#pragma once
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#include <DB/IO/VarInt.h>
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#include <DB/DataTypes/DataTypesNumberFixed.h>
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#include <DB/AggregateFunctions/INullaryAggregateFunction.h>
namespace DB
{
struct AggregateFunctionCountData
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{
UInt64 count;
AggregateFunctionCountData() : count(0) {}
};
/// Просто считает, сколько раз её вызвали
class AggregateFunctionCount final : public INullaryAggregateFunction<AggregateFunctionCountData, AggregateFunctionCount>
{
public:
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String getName() const override { return "count"; }
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DataTypePtr getReturnType() const override
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{
return std::make_shared<DataTypeUInt64>();
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}
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void addImpl(AggregateDataPtr place) const
{
++data(place).count;
}
void merge(AggregateDataPtr place, ConstAggregateDataPtr rhs, Arena * arena) const override
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{
data(place).count += data(rhs).count;
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}
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void serialize(ConstAggregateDataPtr place, WriteBuffer & buf) const override
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{
writeVarUInt(data(place).count, buf);
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}
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void deserialize(AggregateDataPtr place, ReadBuffer & buf, Arena *) const override
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{
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readVarUInt(data(place).count, buf);
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}
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void insertResultInto(ConstAggregateDataPtr place, IColumn & to) const override
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{
static_cast<ColumnUInt64 &>(to).getData().push_back(data(place).count);
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}
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/// Для оптимизации
void addDelta(AggregateDataPtr place, UInt64 x) const
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{
data(place).count += x;
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}
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};
}