ClickHouse/dbms/src/DataStreams/MaterializingBlockInputStream.cpp

#include <DB/DataStreams/MaterializingBlockInputStream.h>
#include <DB/Columns/ColumnConst.h>
#include <DB/DataTypes/DataTypeNullable.h>
#include <DB/DataTypes/DataTypesNumberFixed.h>

namespace DB
{

MaterializingBlockInputStream::MaterializingBlockInputStream(BlockInputStreamPtr input_)
{
	children.push_back(input_);
}

String MaterializingBlockInputStream::getName() const
{
	return "Materializing";
}

String MaterializingBlockInputStream::getID() const
{
	std::stringstream res;
	res << "Materializing(" << children.back()->getID() << ")";
	return res.str();
}

Block MaterializingBlockInputStream::readImpl()
{
	Block res = children.back()->read();

	if (!res)
		return res;

	size_t columns = res.columns();
	for (size_t i = 0; i < columns; ++i)
	{
		auto & element = res.getByPosition(i);
		auto & src = element.column;
		ColumnPtr converted = src->convertToFullColumnIfConst();
		if (converted)
		{
			src = converted;
			auto & type = element.type;
			if (type.get()->isNull())
			{
				/// A ColumnNull that is converted to a full column
				/// has the type DataTypeNullable(DataTypeUInt8).
				type = std::make_shared<DataTypeNullable>(std::make_shared<DataTypeUInt8>());
			}
		}
	}

	return res;
}

}