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