mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-13 19:14:30 +00:00
53 lines
1.4 KiB
C++
53 lines
1.4 KiB
C++
#pragma once
|
|
|
|
#include <DataStreams/IBlockInputStream.h>
|
|
#include <Interpreters/SetVariants.h>
|
|
|
|
namespace DB
|
|
{
|
|
|
|
/** This class is intended for implementation of SELECT DISTINCT clause and
|
|
* leaves only unique rows in the stream.
|
|
*
|
|
* To optimize the SELECT DISTINCT ... LIMIT clause we can
|
|
* set limit_hint to non zero value. So we stop emitting new rows after
|
|
* count of already emitted rows will reach the limit_hint.
|
|
*/
|
|
class DistinctBlockInputStream : public IBlockInputStream
|
|
{
|
|
public:
|
|
/// Empty columns_ means all collumns.
|
|
DistinctBlockInputStream(const BlockInputStreamPtr & input, const SizeLimits & set_size_limits_, UInt64 limit_hint_, const Names & columns_);
|
|
|
|
String getName() const override { return "Distinct"; }
|
|
|
|
Block getHeader() const override { return children.at(0)->getHeader(); }
|
|
|
|
protected:
|
|
Block readImpl() override;
|
|
|
|
private:
|
|
ColumnRawPtrs getKeyColumns(const Block & block) const;
|
|
|
|
template <typename Method>
|
|
void buildFilter(
|
|
Method & method,
|
|
const ColumnRawPtrs & key_columns,
|
|
IColumn::Filter & filter,
|
|
size_t rows,
|
|
SetVariants & variants) const;
|
|
|
|
|
|
Names columns_names;
|
|
SetVariants data;
|
|
Sizes key_sizes;
|
|
UInt64 limit_hint;
|
|
|
|
bool no_more_rows = false;
|
|
|
|
/// Restrictions on the maximum size of the output data.
|
|
SizeLimits set_size_limits;
|
|
};
|
|
|
|
}
|