Function convertTypeToNullable

src/Interpreters/join_common.cpp:88–104

Add nullability to type. Note: LowCardinality(T) transformed to LowCardinality(Nullable(T))

/// Add nullability to type.
/// Note: LowCardinality(T) transformed to LowCardinality(Nullable(T))
DataTypePtr convertTypeToNullable(const DataTypePtr & type)
{
    if (isNullable(type))
        return type;

    if (const auto * low_cardinality_type = typeid_cast<const DataTypeLowCardinality *>(type.get()))
    {
        const auto & dict_type = low_cardinality_type->getDictionaryType();
        if (dict_type->canBeInsideNullable())
            return std::make_shared<DataTypeLowCardinality>(makeNullable(dict_type));
    }

    if (type->canBeInsideNullable())
        return makeNullable(type);

    return type;
}


DataTypePtr tryConvertTypeToNullable(const DataTypePtr & type)