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#include <Functions/IFunction.h>
#include <Functions/FunctionHelpers.h>
#include <Functions/FunctionFactory.h>
#include <DataTypes/DataTypesNumber.h>
#include <Core/ColumnNumbers.h>
#include <Columns/ColumnNullable.h>
#include <Columns/ColumnLowCardinality.h>
namespace DB
{
namespace
{
/// Implements the function isNull which returns true if a value
/// is null, false otherwise.
class FunctionIsNull : public IFunction
{
public:
static constexpr auto name = "isNull";
static FunctionPtr create(ContextPtr)
{
return std::make_shared<FunctionIsNull>();
}
std::string getName() const override
{
return name;
}
size_t getNumberOfArguments() const override { return 1; }
bool useDefaultImplementationForNulls() const override { return false; }
bool useDefaultImplementationForLowCardinalityColumns() const override { return false; }
bool useDefaultImplementationForConstants() const override { return true; }
bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }
ColumnNumbers getArgumentsThatDontImplyNullableReturnType(size_t /*number_of_arguments*/) const override { return {0}; }
DataTypePtr getReturnTypeImpl(const DataTypes &) const override
{
return std::make_shared<DataTypeUInt8>();
}
ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t) const override
{
const ColumnWithTypeAndName & elem = arguments[0];
if (elem.type->isLowCardinalityNullable())
{
const auto * low_cardinality_column = checkAndGetColumn<ColumnLowCardinality>(*elem.column);
size_t null_index = low_cardinality_column->getDictionary().getNullValueIndex();
auto res = DataTypeUInt8().createColumn();
auto & data = typeid_cast<ColumnUInt8 &>(*res).getData();
data.reserve(low_cardinality_column->size());
for (size_t i = 0; i != low_cardinality_column->size(); ++i)
data.push_back(low_cardinality_column->getIndexAt(i) == null_index);
return res;
}
if (const auto * nullable = checkAndGetColumn<ColumnNullable>(*elem.column))
{
/// Merely return the embedded null map.
return nullable->getNullMapColumnPtr();
}
else
{
/// Since no element is nullable, return a zero-constant column representing
/// a zero-filled null map.
return DataTypeUInt8().createColumnConst(elem.column->size(), 0u);
}
}
};
}
REGISTER_FUNCTION(IsNull)
{
factory.registerFunction<FunctionIsNull>({}, FunctionFactory::CaseInsensitive);
}
}
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