ClickHouse/dbms/src/DataStreams/AddingConstColumnBlockInputStream.h

#pragma once

#include <DataStreams/IProfilingBlockInputStream.h>
#include <Columns/ColumnConst.h>
#include <Core/ColumnWithTypeAndName.h>

namespace DB
{

/** Добавляет в блок материализованный const column с заданным значением.
  */
template <typename ColumnType>
class AddingConstColumnBlockInputStream : public IProfilingBlockInputStream
{
public:
    AddingConstColumnBlockInputStream(
        BlockInputStreamPtr input_,
        DataTypePtr data_type_,
        ColumnType value_,
        String column_name_)
        : data_type(data_type_), value(value_), column_name(column_name_)
    {
        children.push_back(input_);
    }

    String getName() const override { return "AddingConstColumn"; }

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

protected:
    Block readImpl() override
    {
        Block res = children.back()->read();
        if (!res)
            return res;
        ColumnPtr column_ptr = ColumnConst<ColumnType>(res.rows(), value, data_type).convertToFullColumn();
        res.insert({column_ptr, data_type, column_name});
        return res;
    }

private:
    DataTypePtr data_type;
    ColumnType value;
    String column_name;
};

}