ClickHouse/dbms/include/DB/DataStreams/ProjectionBlockInputStream.h
2012-10-20 02:10:47 +00:00

55 lines
1.4 KiB
C++

#pragma once
#include <Poco/SharedPtr.h>
#include <DB/Interpreters/Expression.h>
#include <DB/DataStreams/IProfilingBlockInputStream.h>
namespace DB
{
using Poco::SharedPtr;
/** Выбирает из блока только столбцы, являющиеся результатом вычисления выражения.
* Следует применять после ExpressionBlockInputStream.
*/
class ProjectionBlockInputStream : public IProfilingBlockInputStream
{
public:
ProjectionBlockInputStream(
BlockInputStreamPtr input_,
ExpressionPtr expression_,
bool without_duplicates_and_aliases_ = false,
unsigned part_id_ = 0,
ASTPtr subtree_ = NULL)
: input(input_), expression(expression_), without_duplicates_and_aliases(without_duplicates_and_aliases_), part_id(part_id_), subtree(subtree_)
{
children.push_back(input);
}
String getName() const { return "ProjectionBlockInputStream"; }
BlockInputStreamPtr clone() { return new ProjectionBlockInputStream(input, expression, without_duplicates_and_aliases, part_id, subtree); }
protected:
Block readImpl()
{
Block res = input->read();
if (!res)
return res;
return expression->projectResult(res, without_duplicates_and_aliases, part_id, subtree);
}
private:
BlockInputStreamPtr input;
ExpressionPtr expression;
bool without_duplicates_and_aliases;
unsigned part_id;
ASTPtr subtree;
};
}