ClickHouse/dbms/src/Columns/ColumnNullable.h

#pragma once

#include <Columns/IColumn.h>
#include <Columns/ColumnsNumber.h>

namespace DB
{

using NullMap = ColumnUInt8::Container;
using ConstNullMapPtr = const NullMap *;

/// Class that specifies nullable columns. A nullable column represents
/// a column, which may have any type, provided with the possibility of
/// storing NULL values. For this purpose, a ColumNullable object stores
/// an ordinary column along with a special column, namely a byte map,
/// whose type is ColumnUInt8. The latter column indicates whether the
/// value of a given row is a NULL or not. Such a design is preferred
/// over a bitmap because columns are usually stored on disk as compressed
/// files. In this regard, using a bitmap instead of a byte map would
/// greatly complicate the implementation with little to no benefits.
class ColumnNullable final : public COWPtrHelper<IColumn, ColumnNullable>
{
private:
    friend class COWPtrHelper<IColumn, ColumnNullable>;

    ColumnNullable(MutableColumnPtr && nested_column_, MutableColumnPtr && null_map_);
    ColumnNullable(const ColumnNullable &) = default;

public:
    /** Create immutable column using immutable arguments. This arguments may be shared with other columns.
      * Use IColumn::mutate in order to make mutable column and mutate shared nested columns.
      */
    using Base = COWPtrHelper<IColumn, ColumnNullable>;
    static Ptr create(const ColumnPtr & nested_column_, const ColumnPtr & null_map_)
    {
        return ColumnNullable::create(nested_column_->assumeMutable(), null_map_->assumeMutable());
    }

    template <typename ... Args, typename = typename std::enable_if<IsMutableColumns<Args ...>::value>::type>
    static MutablePtr create(Args &&... args) { return Base::create(std::forward<Args>(args)...); }

    const char * getFamilyName() const override { return "Nullable"; }
    std::string getName() const override { return "Nullable(" + nested_column->getName() + ")"; }
    MutableColumnPtr cloneResized(size_t size) const override;
    size_t size() const override { return nested_column->size(); }
    bool isNullAt(size_t n) const override { return static_cast<const ColumnUInt8 &>(*null_map).getData()[n] != 0;}
    Field operator[](size_t n) const override;
    void get(size_t n, Field & res) const override;
    UInt8 getBoolRepresentation(size_t n) const override { return isNullAt(n) ? 0 : nested_column->getBoolRepresentation(n); }
    UInt64 get64(size_t n) const override { return nested_column->get64(n); }
    StringRef getDataAt(size_t n) const override;
    void insertData(const char * pos, size_t length) override;
    StringRef serializeValueIntoArena(size_t n, Arena & arena, char const *& begin) const override;
    const char * deserializeAndInsertFromArena(const char * pos) override;
    void insertRangeFrom(const IColumn & src, size_t start, size_t length) override;;
    void insert(const Field & x) override;
    void insertFrom(const IColumn & src, size_t n) override;

    void insertDefault() override
    {
        getNestedColumn().insertDefault();
        getNullMapData().push_back(1);
    }

    void popBack(size_t n) override;
    ColumnPtr filter(const Filter & filt, ssize_t result_size_hint) const override;
    ColumnPtr permute(const Permutation & perm, size_t limit) const override;
    int compareAt(size_t n, size_t m, const IColumn & rhs_, int null_direction_hint) const override;
    void getPermutation(bool reverse, size_t limit, int null_direction_hint, Permutation & res) const override;
    void reserve(size_t n) override;
    size_t byteSize() const override;
    size_t allocatedBytes() const override;
    ColumnPtr replicate(const Offsets & replicate_offsets) const override;
    void updateHashWithValue(size_t n, SipHash & hash) const override;
    void getExtremes(Field & min, Field & max) const override;

    MutableColumns scatter(ColumnIndex num_columns, const Selector & selector) const override
    {
        return scatterImpl<ColumnNullable>(num_columns, selector);
    }

    void gather(ColumnGathererStream & gatherer_stream) override;

    void forEachSubcolumn(ColumnCallback callback) override
    {
        callback(nested_column);
        callback(null_map);
    }

    bool isColumnNullable() const override { return true; }
    bool isFixedAndContiguous() const override { return false; }
    bool valuesHaveFixedSize() const override { return nested_column->valuesHaveFixedSize(); }
    size_t sizeOfValueIfFixed() const override { return null_map->sizeOfValueIfFixed() + nested_column->sizeOfValueIfFixed(); }
    bool onlyNull() const override { return nested_column->isDummy(); }


    /// Return the column that represents values.
    IColumn & getNestedColumn() { return nested_column->assumeMutableRef(); }
    const IColumn & getNestedColumn() const { return *nested_column; }

    const ColumnPtr & getNestedColumnPtr() const { return nested_column; }

    /// Return the column that represents the byte map.
    //ColumnPtr & getNullMapColumnPtr() { return null_map; }
    const ColumnPtr & getNullMapColumnPtr() const { return null_map; }

    ColumnUInt8 & getNullMapColumn() { return static_cast<ColumnUInt8 &>(null_map->assumeMutableRef()); }
    const ColumnUInt8 & getNullMapColumn() const { return static_cast<const ColumnUInt8 &>(*null_map); }

    NullMap & getNullMapData() { return getNullMapColumn().getData(); }
    const NullMap & getNullMapData() const { return getNullMapColumn().getData(); }

    /// Apply the null byte map of a specified nullable column onto the
    /// null byte map of the current column by performing an element-wise OR
    /// between both byte maps. This method is used to determine the null byte
    /// map of the result column of a function taking one or more nullable
    /// columns.
    void applyNullMap(const ColumnNullable & other);
    void applyNullMap(const ColumnUInt8 & map);
    void applyNegatedNullMap(const ColumnUInt8 & map);

    /// Check that size of null map equals to size of nested column.
    void checkConsistency() const;

private:
    ColumnPtr nested_column;
    ColumnPtr null_map;

    template <bool negative>
    void applyNullMapImpl(const ColumnUInt8 & map);
};


ColumnPtr makeNullable(const ColumnPtr & column);

}