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#pragma once
#include <Functions/IFunction.h>
#include <Functions/FunctionFactory.h>
#include <Interpreters/Context.h>
namespace DB
{
/// Base class for constant functions
template<typename Derived, typename T, typename ColumnT>
class FunctionConstantBase : public IFunction
{
public:
template <typename U>
explicit FunctionConstantBase(U && constant_value_, bool is_distributed_ = false)
: constant_value(static_cast<T>(std::forward<U>(constant_value_))), is_distributed(is_distributed_)
{
}
String getName() const override
{
return Derived::name;
}
size_t getNumberOfArguments() const override
{
return 0;
}
DataTypePtr getReturnTypeImpl(const DataTypes & /*arguments*/) const override
{
return std::make_shared<ColumnT>();
}
bool isDeterministic() const override { return false; }
/// Some functions may return different values on different shards/replicas, so it's not constant for distributed query
bool isSuitableForConstantFolding() const override { return !is_distributed; }
bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }
ColumnPtr executeImpl(const ColumnsWithTypeAndName &, const DataTypePtr & result_type, size_t input_rows_count) const override
{
return result_type->createColumnConst(input_rows_count, constant_value);
}
private:
const T constant_value;
bool is_distributed;
};
}
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