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

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#pragma once
#include <DB/AggregateFunctions/IAggregateFunction.h>
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#include <DB/DataTypes/IDataType.h>
#include <boost/iterator/transform_iterator.hpp>
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namespace DB
{
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/** Creates an aggregate function by name.
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*/
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class AggregateFunctionFactory final
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{
friend class StorageSystemFunctions;
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private:
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/// No std::function, for smaller object size and less indirection.
using Creator = AggregateFunctionPtr(*)(const String & name, const DataTypes & argument_types);
using AggregateFunctions = std::unordered_map<String, Creator>;
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public:
AggregateFunctionFactory();
AggregateFunctionPtr get(const String & name, const DataTypes & argument_types, int recursion_level = 0) const;
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AggregateFunctionPtr tryGet(const String & name, const DataTypes & argument_types) const;
bool isAggregateFunctionName(const String & name, int recursion_level = 0) const;
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/// For compatibility with SQL, it's possible to specify that certain aggregate function name is case insensitive.
enum CaseSensitiveness
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{
CaseSensitive,
CaseInsensitive
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};
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/// Register an aggregate function by its name.
void registerFunction(const String & name, Creator creator, CaseSensitiveness case_sensitiveness = CaseSensitive);
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AggregateFunctionFactory(const AggregateFunctionFactory &) = delete;
AggregateFunctionFactory & operator=(const AggregateFunctionFactory &) = delete;
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private:
AggregateFunctionPtr getImpl(const String & name, const DataTypes & argument_types, int recursion_level) const;
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private:
AggregateFunctions aggregate_functions;
/// Case insensitive aggregate functions will be additionally added here with lowercased name.
AggregateFunctions case_insensitive_aggregate_functions;
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};
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}