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

68 lines
1.1 KiB
C++

#pragma once
#include <DB/IO/WriteHelpers.h>
#include <DB/IO/ReadHelpers.h>
#include <DB/DataTypes/DataTypesNumberFixed.h>
#include <DB/AggregateFunctions/INullaryAggregateFunction.h>
namespace DB
{
/// Просто считает, сколько раз её вызвали
class AggregateFunctionCount : public INullaryAggregateFunction
{
private:
UInt64 count;
public:
AggregateFunctionCount() : count(0) {}
String getName() const { return "count"; }
String getTypeID() const { return "count"; }
AggregateFunctionPlainPtr cloneEmpty() const
{
return new AggregateFunctionCount;
}
DataTypePtr getReturnType() const
{
return new DataTypeUInt64;
}
void addZero() { ++count; }
void merge(const IAggregateFunction & rhs)
{
count += static_cast<const AggregateFunctionCount &>(rhs).count;
}
void serialize(WriteBuffer & buf) const
{
writeVarUInt(count, buf);
}
void deserializeMerge(ReadBuffer & buf)
{
UInt64 tmp;
readVarUInt(tmp, buf);
count += tmp;
}
Field getResult() const
{
return count;
}
/// Для оптимизации
void addDelta(UInt64 x)
{
count += x;
}
};
}