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30 lines
662 B
C++
30 lines
662 B
C++
#pragma once
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#include <Processors/ISimpleTransform.h>
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#include <Common/HashTable/HashMap.h>
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namespace DB
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{
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/// Executes LIMIT BY for specified columns.
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class LimitByTransform : public ISimpleTransform
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{
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public:
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LimitByTransform(const Block & header, UInt64 group_length_, UInt64 group_offset_, const Names & columns);
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String getName() const override { return "LimitByTransform"; }
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protected:
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void transform(Chunk & chunk) override;
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private:
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using MapHashed = HashMap<UInt128, UInt64, UInt128TrivialHash>;
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MapHashed keys_counts;
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std::vector<size_t> key_positions;
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const UInt64 group_length;
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const UInt64 group_offset;
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};
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}
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