Function initializeTransformCache

src/Functions/transform.cpp:711–844

Initialize the transform cache from the constant arguments.

    /// Initialize the transform cache from the constant arguments.
    TransformCachePtr initializeTransformCache(const ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type)
    {
        auto cache = std::make_shared<TransformCache>();

        const DataTypePtr & from_type = arguments[0].type;

        if (from_type->onlyNull())
        {
            cache->is_empty = true;
            return cache;
        }

        const ColumnArray * array_from = checkAndGetColumnConstData<ColumnArray>(arguments[1].column.get());
        const ColumnArray * array_to = checkAndGetColumnConstData<ColumnArray>(arguments[2].column.get());

        if (!array_from || !array_to)
            throw Exception(
                ErrorCodes::ILLEGAL_COLUMN, "Second and third arguments of function {} must be constant arrays", "transform");

        const ColumnPtr & from_column_uncast = array_from->getDataPtr();

        cache->from_column = castColumn(
            {
                from_column_uncast,
                typeid_cast<const DataTypeArray &>(*arguments[1].type).getNestedType(),
                arguments[1].name
            },
            from_type);

        cache->to_column = castColumn(
            {
                array_to->getDataPtr(),
                typeid_cast<const DataTypeArray &>(*arguments[2].type).getNestedType(),
                arguments[2].name
            },
            result_type);

        const size_t size = cache->from_column->size();
        if (0 == size)
        {
            cache->is_empty = true;
            return cache;
        }

        if (cache->to_column->size() != size)
            throw Exception(
                ErrorCodes::BAD_ARGUMENTS, "Second and third arguments of function {} must be arrays of same size", "transform");

        /// Whether the default value is set.
        if (arguments.size() == 4)
        {
            const IColumn * default_col = arguments[3].column.get();
            if (default_col && isColumnConst(*default_col))
            {
                if (default_col->onlyNull())
                {
                    auto default_column = result_type->createColumn();
                    default_column->insertDefault();