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#include <Functions/IFunction.h>
#include <Functions/FunctionFactory.h>
#include <DataTypes/DataTypesNumber.h>
#include <Columns/ColumnsNumber.h>
namespace DB
{
namespace
{
/// Returns 1 if and only if the argument is constant expression.
/// This function exists for development, debugging and demonstration purposes.
class FunctionIsConstant : public IFunction
{
public:
static constexpr auto name = "isConstant";
static FunctionPtr create(ContextPtr)
{
return std::make_shared<FunctionIsConstant>();
}
String getName() const override
{
return name;
}
bool useDefaultImplementationForNulls() const override { return false; }
bool useDefaultImplementationForNothing() const override { return false; }
bool useDefaultImplementationForLowCardinalityColumns() const override { return false; }
bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }
size_t getNumberOfArguments() const override
{
return 1;
}
DataTypePtr getReturnTypeImpl(const DataTypes & /*arguments*/) const override
{
return std::make_shared<DataTypeUInt8>();
}
ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t input_rows_count) const override
{
const auto & elem = arguments[0];
return ColumnUInt8::create(input_rows_count, isColumnConst(*elem.column));
}
};
}
REGISTER_FUNCTION(IsConstant)
{
factory.registerFunction<FunctionIsConstant>();
}
}
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