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68 lines
2.1 KiB
C++
68 lines
2.1 KiB
C++
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#pragma once
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#include <DataStreams/IProfilingBlockInputStream.h>
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#include <Interpreters/Limits.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 DistinctSortedBlockInputStream : public IProfilingBlockInputStream
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{
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public:
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/// Empty columns_ means all collumns.
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DistinctSortedBlockInputStream(BlockInputStreamPtr input_, const Limits & limits, size_t limit_hint_, Names columns_);
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String getName() const override { return "DistinctSorted"; }
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String getID() const override;
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protected:
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Block readImpl() override;
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private:
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bool checkLimits() const;
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ConstColumnPlainPtrs getKeyColumns(const Block & block) const;
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/// When clearing_columns changed, we can clean HashSet to memory optimization
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/// clearing_columns is a left-prefix of SortDescription exists in key_columns
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ConstColumnPlainPtrs getClearingColumns(const Block & block, const ConstColumnPlainPtrs & key_columns) const;
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static bool rowsEqual(const ConstColumnPlainPtrs & lhs, size_t n, const ConstColumnPlainPtrs & rhs, size_t m);
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/// return true if has new data
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template <typename Method>
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bool buildFilter(
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Method & method,
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const ConstColumnPlainPtrs & key_columns,
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const ConstColumnPlainPtrs & clearing_hint_columns,
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IColumn::Filter & filter,
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size_t rows,
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ClearableSetVariants & variants) const;
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const SortDescription& description;
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struct PreviousBlock
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{
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Block block;
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ConstColumnPlainPtrs clearing_hint_columns;
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} prev_block;
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Names columns_names;
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ClearableSetVariants data;
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Sizes key_sizes;
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size_t limit_hint;
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/// Restrictions on the maximum size of the output data.
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size_t max_rows;
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size_t max_bytes;
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OverflowMode overflow_mode;
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};
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}
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