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53 lines
1.3 KiB
C++
53 lines
1.3 KiB
C++
#pragma once
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#include <DataStreams/IBlockInputStream.h>
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#include <Interpreters/SetVariants.h>
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namespace DB
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{
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/** This class is intended for implementation of SELECT DISTINCT clause and
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* leaves only unique rows in the stream.
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*
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* To optimize the SELECT DISTINCT ... LIMIT clause we can
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* set limit_hint to non zero value. So we stop emitting new rows after
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* count of already emitted rows will reach the limit_hint.
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*/
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class DistinctBlockInputStream : public IBlockInputStream
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{
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public:
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/// Empty columns_ means all collumns.
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DistinctBlockInputStream(const BlockInputStreamPtr & input, const SizeLimits & set_size_limits, UInt64 limit_hint_, const Names & columns);
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String getName() const override { return "Distinct"; }
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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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ColumnRawPtrs getKeyColumns(const Block & block) const;
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template <typename Method>
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void buildFilter(
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Method & method,
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const ColumnRawPtrs & key_columns,
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IColumn::Filter & filter,
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size_t rows,
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SetVariants & variants) const;
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Names columns_names;
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SetVariants data;
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Sizes key_sizes;
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UInt64 limit_hint;
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bool no_more_rows = false;
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/// Restrictions on the maximum size of the output data.
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SizeLimits set_size_limits;
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};
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}
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