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48 lines
1.6 KiB
C++
48 lines
1.6 KiB
C++
#pragma once
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#include <DataStreams/IBlockInputStream.h>
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#include <Common/SharedBlockRowRef.h>
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#include <Core/SortDescription.h>
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namespace DB
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{
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/** Implements the LIMIT relational operation.
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*/
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class LimitBlockInputStream : public IBlockInputStream
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{
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public:
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/** If always_read_till_end = false (by default), then after reading enough data,
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* returns an empty block, and this causes the query to be canceled.
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* If always_read_till_end = true - reads all the data to the end, but ignores them. This is necessary in rare cases:
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* when otherwise, due to the cancellation of the request, we would not have received the data for GROUP BY WITH TOTALS from the remote server.
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* If use_limit_as_total_rows_approx = true, then addTotalRowsApprox is called to use the limit in progress & stats
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* with_ties = true, when query has WITH TIES modifier. If so, description should be provided
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* description lets us know which row we should check for equality
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*/
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LimitBlockInputStream(
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const BlockInputStreamPtr & input, UInt64 limit_, UInt64 offset_,
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bool always_read_till_end_ = false, bool use_limit_as_total_rows_approx = false,
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bool with_ties_ = false, const SortDescription & description_ = {});
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String getName() const override { return "Limit"; }
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Block getHeader() const override { return children.at(0)->getHeader(); }
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protected:
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Block readImpl() override;
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private:
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UInt64 limit;
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UInt64 offset;
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UInt64 pos = 0;
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bool always_read_till_end;
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bool with_ties;
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const SortDescription description;
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SharedBlockRowRef ties_row_ref;
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};
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}
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