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45 lines
1011 B
C++
45 lines
1011 B
C++
#pragma once
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#include <Poco/SharedPtr.h>
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#include <DB/Interpreters/Expression.h>
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#include <DB/DataStreams/IBlockInputStream.h>
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namespace DB
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{
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using Poco::SharedPtr;
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/** Выбирает из блока только столбцы, являющиеся результатом вычисления выражения.
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* Следует применять после ExpressionBlockInputStream.
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*/
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class ProjectionBlockInputStream : public IBlockInputStream
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{
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public:
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ProjectionBlockInputStream(
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BlockInputStreamPtr input_,
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SharedPtr<Expression> expression_,
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bool without_duplicates_ = false,
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unsigned part_id_ = 0)
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: input(input_), expression(expression_), without_duplicates(without_duplicates_), part_id(part_id_) {}
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Block read()
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{
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Block res = input->read();
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if (!res)
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return res;
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return expression->projectResult(res, without_duplicates, part_id);
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}
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private:
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BlockInputStreamPtr input;
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SharedPtr<Expression> expression;
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bool without_duplicates;
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unsigned part_id;
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};
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}
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