ClickHouse/dbms/src/DataStreams/NullAndDoCopyBlockInputStream.h

46 lines
1.2 KiB
C++

#pragma once
#include <DataStreams/IBlockInputStream.h>
#include <DataStreams/copyData.h>
namespace DB
{
class IBlockOutputStream;
using BlockOutputStreamPtr = std::shared_ptr<IBlockOutputStream>;
/** An empty stream of blocks.
* But at the first read attempt, copies the data from the passed `input` to the `output`.
* This is necessary to execute the query INSERT SELECT - the query copies data, but returns nothing.
* The query could be executed without wrapping it in an empty BlockInputStream,
* but the progress of query execution and the ability to cancel the query would not work.
*/
class NullAndDoCopyBlockInputStream : public IBlockInputStream
{
public:
NullAndDoCopyBlockInputStream(const BlockInputStreamPtr & input_, BlockOutputStreamPtr output_)
: input(input_), output(output_)
{
children.push_back(input_);
}
String getName() const override { return "NullAndDoCopy"; }
Block getHeader() const override { return {}; }
protected:
Block readImpl() override
{
copyData(*input, *output);
return Block();
}
private:
BlockInputStreamPtr input;
BlockOutputStreamPtr output;
};
}