ClickHouse/src/DataTypes/DataTypeNullable.h

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#pragma once
#include <DataTypes/IDataType.h>
namespace DB
{
/// A nullable data type is an ordinary data type provided with a tag
/// indicating that it also contains the NULL value. The following class
/// embodies this concept.
class DataTypeNullable final : public IDataType
{
public:
static constexpr bool is_parametric = true;
explicit DataTypeNullable(const DataTypePtr & nested_data_type_);
std::string doGetName() const override { return "Nullable(" + nested_data_type->getName() + ")"; }
const char * getFamilyName() const override { return "Nullable"; }
TypeIndex getTypeId() const override { return TypeIndex::Nullable; }
MutableColumnPtr createColumn() const override;
Field getDefault() const override;
bool equals(const IDataType & rhs) const override;
bool isParametric() const override { return true; }
bool haveSubtypes() const override { return true; }
bool cannotBeStoredInTables() const override { return nested_data_type->cannotBeStoredInTables(); }
bool shouldAlignRightInPrettyFormats() const override { return nested_data_type->shouldAlignRightInPrettyFormats(); }
bool textCanContainOnlyValidUTF8() const override { return nested_data_type->textCanContainOnlyValidUTF8(); }
bool isComparable() const override { return nested_data_type->isComparable(); }
bool canBeComparedWithCollation() const override { return nested_data_type->canBeComparedWithCollation(); }
bool canBeUsedAsVersion() const override { return false; }
bool isSummable() const override { return nested_data_type->isSummable(); }
bool canBeUsedInBooleanContext() const override { return nested_data_type->canBeUsedInBooleanContext() || onlyNull(); }
bool haveMaximumSizeOfValue() const override { return nested_data_type->haveMaximumSizeOfValue(); }
size_t getMaximumSizeOfValueInMemory() const override { return 1 + nested_data_type->getMaximumSizeOfValueInMemory(); }
bool isNullable() const override { return true; }
size_t getSizeOfValueInMemory() const override;
bool onlyNull() const override;
bool canBeInsideLowCardinality() const override { return nested_data_type->canBeInsideLowCardinality(); }
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bool canBePromoted() const override { return nested_data_type->canBePromoted(); }
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const DataTypePtr & getNestedType() const { return nested_data_type; }
private:
SerializationPtr doGetDefaultSerialization() const override;
DataTypePtr nested_data_type;
};
DataTypePtr makeNullable(const DataTypePtr & type);
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DataTypePtr makeNullableSafe(const DataTypePtr & type);
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DataTypePtr removeNullable(const DataTypePtr & type);
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DataTypePtr makeNullableOrLowCardinalityNullable(const DataTypePtr & type);
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DataTypePtr makeNullableOrLowCardinalityNullableSafe(const DataTypePtr & type);
/// Nullable(T) -> T, LowCardinality(Nullable(T)) -> T
DataTypePtr removeNullableOrLowCardinalityNullable(const DataTypePtr & type);
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}