ClickHouse/dbms/include/DB/DataStreams/ProjectionBlockInputStream.h

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